Progress 02/15/20 to 02/14/21
Outputs
Target Audience:This information is duplicated in the final report for this project. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Two undergraduates performed research in the laboratory towards the objectives of this project. These are Mr. Owen Long and Mr. Carter Newton. How have the results been disseminated to communities of interest?This information is provided in the final project report. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
This information is provided in detail in the final project report.
Publications
- Type:
Journal Articles
Status:
Other
Year Published:
2021
Citation:
Shuler, S.L., Hennen-Bierwagen, T.A., Tracy, W.F., and Myers, A.M. (2021)The non-catalytic ?(1?6) glucosidase homolog ISA2 modifies starch and phytoglycogen biosynthesis in sweet corn endosperm. Manuscript in preparation for submission in fall 2021.
- Type:
Journal Articles
Status:
Other
Year Published:
2021
Citation:
Hennen-Bierwagen, T.A., Newton, C., Juhl, E., and Myers, A.M. (2021) Novel allelic combinations that cause accumulation of phytoglycogen and elevated sucrose levels in maize endosperm. Manuscript in preparation for submission in fall 2021.
- Type:
Journal Articles
Status:
Published
Year Published:
2021
Citation:
Hu, Y., Colantonio, V., M�ller, B.S.F., Leach, K., Nanni, A., Finegan, C., Wang, B., Baseggio, M., Newton, C.J., Juhl, E.M., Hislop, L., Gonzalez, J.M., Rios, E.F., Hannah, L.C., Swarts, K., Gore, M.A., Hennen-Bierwagen, T.A., Myers, A.M., Settles, A.M., Tracy, W.F., and Resende, M. (2021) Chromosome-scale genome assembly and population genomic analysis provide insights into the origin and evolution of modern sweet corn. Nat. Commun. 12, 1227. (doi: 10.1038/s41467-021-21380-4)
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Progress 02/15/17 to 02/14/21
Outputs
Target Audience:One target audience for these research results is plant breeders potentially interested in developing new types of phytoglycogen-containingsweet corn lines that are not based on the su1-Ref allele that currently is the basis for the large majority of phytoglycogen-containing varieties. Previously undescribed alleles at the su1 locus were characterized for phytoglycogen and sucrose content, and these could be considered for introgression into breeding programs. Also mutations and other loci besides su1 that cause accumulation of phytoglycogen and sugars were characterized, providing the ability to generate sweet corn lines with entirely different genetic basis than is currently used in the industry. Another target audience isfundamental researchers investigating the molecular mechanisms of starch biogenesis. This process is fundamental to plant physiology, and much remains to be understood about how plants accomplish the central aspect of their metabolism. There is an active research field investing starch biosynthetic mechanisms, and the results from this project provide novel information pertinent to how starch is assembled and how that biosynthetic pathway arose during evolution of the plant kingdom. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The project has employed and funded two graduate students per year for the four year period of the award. These are Brianna Allen, Emily Juhl, Carter Newton, and Owen Long The students are majoring in either Genetic or Biochemistry. Ms. Juhl is currently pursuing a Ph.D. in Plant Breeding at the University of Minnesota. Mr. Newton is in the process of applying to Ph.D. programs in plant sciences, focusing on plant-pathogen interactions. Mr. Long is still and undergraduate and continues to perform research in the project laboratory. A graduate student who worked on the project in collaborative capacity but was not funded directly by the NIFA program, Ms. Stacie Shuler, completed her Ph.D. and has moved to a position as a sweet corn breeder with Syngenta. How have the results been disseminated to communities of interest?One peer reviewed publication is competed (Hu et al.). Two additional publication are in preparation at the time of submitting this report, that will be submitted for publication in the fall of 2021, One paper is planned for submission fo Journal of Experimental Botany, and the second is planned for submission to Crop Science. Three research presentations or posters have been given at national meetings, either the Starch Round Table, or the annual meeting of the National Association of Plant Breeders. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Objectives 1 and 2 have been satisfactorily completed. The new germplasm listed in the "Other Products" section of this report is the result of these objectives. Various alleles of the su1 locus other than the commonly used allele in the sweet corn industry, su1-Ref, were bred into two different inbred backgrounds. These are W64A, a line used frequently in fundamental research in maize, and Ia453, an inbred background derived from commercial sweet corn lines. Also bred into these two lines were allelic combination that affect sweet corn characterisitics as a synthetic phenotype requiring changes at two different loci. Essentially, all of thealleles and allelic combinations that are reported here mimic the endosperm tissue phenotype of su1-Ref mutants. The key point is that their derivation is entirely independent of su1-Ref. Thus, any deleterious alleles that may be linked to su1-Ref will not be present in the novel germplasm reported here. This is significant because the genetic basis of su1-Ref is limited, in part becuase the frequency of recombination on the chromosome arm that contains the su1 locus is low compared to the rest of the maize genome. This latter fact is reported in the publication by Hu et al., 2021, reported in the Publications section of this report. The data collected for objectives 1 and 2 include pedigrees of breeding schemes, molecular data that characterize the causative agents of the novel alleles of su1, and most prominently carbohydrate analysis of the finished lines. Most of the characterizations were done on W64A/Ia453 F1 hybrids, so as to mimic hybrid vigor that might occur in a production context. Carbohydrate characterization separated soluble and insoluble glucan polysaccharides and quantified those compounds in comparison to control strains containing the su1-Ref allele. Impact statement for objectives 1 and 2: This research has provided a change in knowledge about the genetic basis of phytoglycogen formation in maize. This chemical feature is the basis of traditional sweet corn lines. Previously almost all characterization of the genetic basis of this trait involved the su1-Ref allele or a null allele, su1-4582. Now we know of additional alleles of su1 that condition phytoglycogen accumulation, which although not quantitatively as extreme as su1-Ref still has the potential to produce quality sweet corns. Also, we know of allelic combinations that do not involve any mutations at the su1 locus but instead combine other lesions within the starch biosynthesis pathway that previously were not known to result in accumulation nof soluble glucan polysaccharide. This new knowledge contributes to our potential to maintain secure production of sweet corn. At this point there is not an acute need for new types of sweet corn, but the genetic bottleneck in the sweet corn industrial lines implies potential dangers should future challenges to crop security arise owing to environmental or biological factors. As yet there have not been changes in condition resulting from this new knowledge. However, the new germplasm availalbe here, which will be publicized in forthcoming peer-reviewed publications, will be freely available to any plant breeders that may wish to pursue introgression into sweet corn breeding programs. Thus in the future there is potential for change in condition, if new sweet corn lines arise that make use the allelic basis that was discovered in this research program. Objective 3 was less developed during the course of the research than objectives 1 and 2. That research required use of extant antibodies, that unfortunately had lost effectiveness during storage and could not be replaced without initiating entirely new immunizations, which were not licensed within the context of this research program. Some molecular characterization was completed, specifically determining the sequence of serveral novel alleles of su1 and assigment of the causative mutation. This work was published in Hu et al., cited in this report.
Publications
- Type:
Journal Articles
Status:
Other
Year Published:
2021
Citation:
Shuler, S.L., Hennen-Bierwagen, T.A., Tracy, W.F., and Myers, A.M. (2021)The non-catalytic ?(1?6) glucosidase homolog ISA2 modifies starch and phytoglycogen biosynthesis in sweet corn endosperm. Manuscript in preparation for submission in fall 2021.
- Type:
Journal Articles
Status:
Other
Year Published:
2021
Citation:
Hennen-Bierwagen, T.A., Newton, C., Juhl, E., and Myers, A.M. (2021) Novel allelic combinations that cause accumulation of phytoglycogen and elevated sucrose levels in maize endosperm. Manuscript in preparation for submission in fall 2021.
- Type:
Journal Articles
Status:
Published
Year Published:
2021
Citation:
Hu, Y., Colantonio, V., M�ller, B.S.F., Leach, K., Nanni, A., Finegan, C., Wang, B., Baseggio, M., Newton, C.J., Juhl, E.M., Hislop, L., Gonzalez, J.M., Rios, E.F., Hannah, L.C., Swarts, K., Gore, M.A., Hennen-Bierwagen, T.A., Myers, A.M., Settles, A.M., Tracy, W.F., and Resende, M. (2021) Chromosome-scale genome assembly and population genomic analysis provide insights into the origin and evolution of modern sweet corn. Nat. Commun. 12, 1227. (doi: 10.1038/s41467-021-21380-4)
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Progress 02/15/19 to 02/14/20
Outputs
Target Audience:The target audiences for this research are 1) plant breeders potentially interested in using the alleles characterized here in breeding programs targeted towards new lines of sweet corn that do not rely on the traditional allele su1-Ref that has long been the basis of phytoglycogen-containing sweet corn lines, and 2) fundamental plant scientists investigating the molecular mechanisms of starch biosythesis in cereal endosperm. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Two undergraduate students performed research in the laboratory towards the objectives of this project. These are Mr. Owen Long, and Mr. Carter Newton. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?The next reporting period is a fourth year that was granted as a no-cost extension to the original project period. This will enable a additional summer nursery that will generate expanded seed stocks. These will be saved as an output of the project, and described to the target audiences in peer-reviewed publication that will be submitted at a later date. There are no restrictions on the use of these materials. They will be offered to the sweet corn breeding community, should any have interest in pursuing their use towards the development of future commericial or reasearch lines.
Impacts
What was accomplished under these goals?
During year three the project came to completion with regard to objectives 1 and 2. A variety of inbreds containing the allelic diversity described in the project description were completed, with four of five backcrosses into two different inbred backgrounds, W64A and Ia453. F1 hybrids were generated by crosses between the two different inbred backgrounds, and these were characterized for soluble and insoluble glucan polysaccharide content as a function of endosperm dry weight. The outcome of this research is a collection of new maize germplasm that causes a high concentration of phytoglycogen in endosperm tissue. This material is listed in the final report.
Publications
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Progress 02/15/18 to 02/14/19
Outputs
Target Audience:As with all reports for this project, one target audience is plant breeders potentially interested in using novel alleles or allelic combinations for introgression into sweet corn backgrounds, replacing the su1-Ref mutation with the new alleles characterized in this study. The second audience is researchers investigating the fundamental biochemical and genetic mechanisms of starch biosynthesis, particularly in cereal endosperm. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Two undergraduate research assistants participated in the project, Mr. Carter Newton and Ms. Emily Juhl. How have the results been disseminated to communities of interest?A poster presentation was given at the 2019 NAPB plant breeding conference. What do you plan to do during the next reporting period to accomplish the goals?Crosses will continue to place a wide variety of su1 alleles, and other alleles that affect the starch biosynthetic process into inbred lines, either in the W64A or Ia453 genetic backgrounds. This process will work towards generation of F1 hybrids that will be tested for chemical consituents that underlie the sweet corn endosperm trait, most importantly the content of soluble glucan polysaccharide.
Impacts
What was accomplished under these goals?
During year two of the project maize breeding continued as described in the project description. The final outcome of this breeding program, in terms of new maize germplasm, is listed in the final project report.
Publications
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Progress 02/15/17 to 02/14/18
Outputs
Target Audience:The reporting period is the first year of the project. The program is still in the breeding stages preliminary to development of final products and reporting of those products to scientific and industry audiences. Therefore, there is nothing to report on target audiences reached during this reporting period. Changes/Problems:The project plans to slightly adjust the number of breeding cycles that are used to create new sweet corn lines that will be tested in a model production environment. The original project proposed five backcrosses of each novel genetic combination that creates sweet corn traits into two separate inbred lines. One of these will be the Ia453 background, which is an inbred derived from a diverse collection of sweet corn land races, and the other is W64A, an inbred useful for biochemical comparisions of sweet corn traits. The minor change that is envisioned is to use backcross 4 lines in each inbred, rather than backcross 5. The backcross 4 lines will be combined in F1 hybrids, and these will be tested for sweet corn traits using the standard assays available in the Tracy laboratory that have been in place for many years. The reason for this change is simply to speed up the time frame of the project within which the novel lines can begin to be evaluated for potential utility in commercial production applications. While the F1 hybrid tests are ongoing, further backcrosses into inbreds will continue, so that preliminary tests in the BC4F1 lines can guide future breeding directions. Another change in the project will be to increase the number of novel genetic combinations that give rise to sweet corn traits that will be tested in the program. Specifically, the program has determined that certain point mutant alleles of the ADPglucose transporter, in combination with certain allels of starch synthase isoforms SSIIa or SSIII, result in kernel phenotypes that strongly indicate sweet corn characteristics. In one instance WSP was specifically identified in the line. These genetic combinations have never been reported previously, or tested to our knowledge, as determinants of sweet corn characteristics. Thus they have been incorporated into the breeding program and will be analyzed in parallel with all of the other mutant combinations that were originally proposed. What opportunities for training and professional development has the project provided?Two undergraduate interns have worked in the project. These are Ms. Briana Allen, who graduated with a B.S. in Genetics in the spring of 2017 and worked on the project through summer 2017, and Ms. Emily Juhl, currently a sophomore majoring in Biochemistry who is still employed on the project. Both interns were trained in maize genetics and participated direclty in the breeding aspects of the program. Both interns also were trainied in molecular biology and biochemistry techniques. Ms. Allen is currently seeking a position in the biotechnolgy industry, and Ms. Juhl is continuing her undergraduate studies at ISU and also continuing her work on the project. One graduate student, Dr. Stacie Shuler, was active in the project during the its first year, through her graduation with the Ph.D. degree in the spring of 2018. Dr. Shuler is currently employed as a sweet corn breeder by Syngenta. A second graduate student, Ms. Baudelia Ruiz , began to work on the plant breeding aspects of the project in spring 2018. How have the results been disseminated to communities of interest?A research seminar describing the results of the project was presented by the PI to the Starch Round Table conference held in San Diego, CA in October 2017. Two manuscripts describing results from the project are currently in preparation. These manuscripts are based on chapters in the Ph.D. thesis of Dr. Shuler that was completed in spring 2018. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period the project will continue the breeding aspects of the program. By the end of the 2019 field season, several BC4F1 hybrid lines will be available as seed, enabling testing of sweet corn characteristics during the successive year of the program (year 3). Other lines will still be in preliminary stages. All breeding will continue as quickly as possible throughout the remainder of the program. Numerous lines are currently available for tesing of biochemical characteristics, both with regard to carbohydrate content and structure and starch biosynthetic enzyme activities. Objectives 2 and 3 of the program will be intensively investigated during the next reporting period.
Impacts
What was accomplished under these goals?
The overall impact of this project, when it is completed, will be availability to sweet corn breeders of new lines with different genetic bases than currently available sweet corn lines. The advantages of these new lines will be twofold. First, the industry will be protected over the long term from future challenges, because diverse collections of sweet corn lines will ensure that some of them will be resistant to unforeseen stresses that may arise, for example, pathogens or sub-optimal environmental. Second, diverse collections of sweet corn lines, with varing genetic bases, will increase the industry's ability to create desirable traits such as mouth feel, sweetness, germination rates, days to maturity, or post-harvest shelf life. The reason that the current sweet corn industry could have need of both impacts is that all extant lines of phytoglycogen-type sweet corn are based on the same narrow collection of genetic variants. The project seeks to expand the number of genetic variants available to the industry. Accomplishments towards meeting achieving these impacts, within each objective of the project, are as follows. Objective 1, Breeding of novel maize inbred germplasm with sweet corn characteristics Genetic combinations bred into the Ia453 genetic background, and the number of backcrosses into that inbred, are as follows. The indicated backcross plants are currently growing in the 2018 field season so the next backcross, after the one indicated below, will be available in seed at the upcoming harvest. Allele or combination Affected enzymes Breeding stage su1-4582 Isoamylase (ISA) 1 deletion BC5 bt1-2859, su2-Ref ADPglucose transporter mutation + starch sythase (SS) IIa mutation BC1 bt1-2859, du-M3 ADPglucose transporter mutation + SSIII deletion BC1 du1-Ref SSIII mutation BC3 bt1-2859, su2-1981 ADPglucose transporter mutation + SSIIa deletion BC1 du1-M3 SSIII deletion BC4 su2-2279 SSIIa deletion BC3 zpu1-204 pullulanase deletion BC4 su1-p ISA1 mutation BC2 su1-st ISA1 mutation BC3 su1-Bn ISA1 mutation BC4 isa2-339 ISAII deletion BC4 du1-M3, su1-p SSIII deletion + ISA1 mutation BC4 du1-Ref, su1-p SSIII mutation + ISA1 mutation BC3 su2-1981, su1-p SSIIa deletion + ISA1 mutation BC3 su1-st, isa2-229 ISA1 mutation + ISA2 deletion BC3 du1-M3, isa2-339 SSIII deletion + ISA2 deletion BC3 du1-M3, su1-st SSIII mutation + ISA1 mutation BC1 su2-2279, su1-st SSIIa deletion + ISA1 mutation BC1 su1-Ref, isa2-339 ISA1 mutation + ISA2 deletion BC5 All of the above genetic combinations are already available in the W64A inbred background. Objective 2, Carbohydrate composition analysis Many of the lines indicated in the table above exhibit shrunken kernels indicative of reduced starch content, increased water-soluble polysaccharide content (WSP), and increased sugar content, i.e., sucrose, glucose, and fructose. WSP has been extracted from each line, and quantified compared to the starch content. The WSP has been characterized by gel permeation chromatography to provide an estimate of the average molecular size and mass of the polymers. As predicted from preliminary data, substantial variability has been noted in the amount of WSP present relative to starch, and average size of the polymers. These distinctions in WSP characteristics are predicted to translate into variability in performance as a sweet corn crop, and this prediction will be tested in the next year of the project. Further detailed characterization of the starches and WSP generated in each mutant line will be performed in the next year of the project, notably determination of the chain length distribution within the glucan polymers. Objective 3, Characterization of starch biosynthetic enzyme activities This aspect of the project will be begun during the next year of the program.
Publications
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