Recipient Organization
PURDUE UNIVERSITY
(N/A)
WEST LAFAYETTE,IN 47907
Performing Department
Agronomy
Non Technical Summary
To feed the increasing world population, it is imperative that we understand how the genetics of the agricultural crops we raise translate into the phenotypes we grow and harvest as well as the traits that provide them resilience to stress and efficiency of resource utilization. Understanding what genes can best be manipulated in plant breeding is an essential part of answering this challenge. The resources we have developed and continue to expand and improve provide a way for breeders to advance their understanding of sorghum genes that control growth, development and output.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Goals / Objectives
The overall goal of this research is to create and make use of collections of mutagenized sorghum lines and diversity panels of germplasm to empower new trait development in sorghum.While two of the three goals are necessarily ongoing processes that continue from past projects, the third goal is the application of these studies to end use.1)Identify and validate the roles of specific sorghum genes and, by extension, genes in maize and other cereal species, in traits of biological, agronomic and economic interest (detailed below) using both "forward" and "reverse" genetic approaches.2)Make these data, materials and resources available to the public.3)Translate this knowledge for new trait development in sorghum breeding populations.
Project Methods
We are characterizing native and induced genetic variants of sorghum to discover genes influencing food and forage quality traits including (1) forage and biomass quality (Krothapalli et al 2013), (2) seed composition and utilization (Massafaro et al., 2016; Griebel et al., 2019a, 2019b), and (3) plant architecture and development (Barrero-Farfan et al., 2012). A workflow has been developed to identify genes and mutations that influence target traits by integrating data from single nucleotide polymorphism identification, prior information about candidate gene(s), and validation of linkage in a mapping population (Krothapalli et al., 2013). This strategy has been adapted to identify genes and alleles for important food and forage quality traits for crop improvement. These genes and alleles will be integrated into the sorghum breeding program. These studies are on-going and will continue in the next phase of this project.1.Improving forage and biomass quality:Dhurrin is a metabolite of sorghum that plays a key role in plant responses to insect feeding, drought tolerance, and nitrogen metabolism.Dhurrin accumulation in sorghum plant tissues negatively impacts forage quality for animal production (Blomstedt et al., 2018; Rosati et al., 2019) and feedstock quality for cellulosic biofuel production (Prasad et al. 2011).Many of the genes and enzymes involved in dhurrin metabolism are known with CYP79A1, CYP71E1, UGT85B1, and POR2b forming a metabolon for synthesis in the ER (Laursen et al., 2016). Raman spectroscopy demonstrated that dhurrin accumulates in epidermal, cortical and vascular tissues in cell walls and cytoplasm in immature shoot tissues (Heraud et al., 2018).The dhurrinases that break down dhurrin to release HCN during insect feeding are found in mesophyll cells (Krothapalli et al., 2013; Nielsen et al., 2016). Other genes including nitrilases and transporters play key roles in alternate dhurrin turnover pathways (Nielsen et al., 2016; Blomstedt et al., 2018).Native and induced genetic variation are being used to modify dhurrin metabolism in sorghum. We used abiochemical assay known as the Fiegle-Anger (FA) Assay to identify genetic variants that do not release HCN. Approximately 50,000 M2 plants were screened to identify mutants impaired in HCN production. Two sorghum mutants were identified (SbEMS2447 and SbEMS5085) that did not produce dhurrin.The mutants were resequenced to identify the candidate genes and mutation(s) in these lines. A C493Y mutation in CYP79A1 was discovered that co-segregated with the HCN- phenotype. Subsequent studies showed that dhurrin-free plants looked normal in multilocation field trials and exhibited no significant differences in performance and biomass production compared to wild-type plants.The C493Y mutation in CYP79A1 is being used in the sorghum breeding program to produce dhurrin-free (DX) sorghum plants (Tuinstra et al., 2016). TheDX trait is being stacked withother important genes and alleles controlling brown mid-rib and forage digestibility (bmr6andbmr12), plant color (pandq), plant height and architecture (dw1,dw2,dw3, anddw4), and maturity (ma1,ma5, andma6)to maximize hay and silage production and quality. A DX seed testing system is being developed with Indiana Crop Improvement Association to enable routine monitoring of DX sorghum seed purity and quality.The Purdue sorghum breeding program began crossing and backcrossing the DX trait (C493Y) into sorghum parent lines that can be used to produce commercial hybrids.We have developed two pollinator parents as well as an A-line and B-line pair for use in seed production. These parents can be combined to produce a sorghum-sudan hybrid and a forage sorghum hybrid.Field trials of experimental DX sorghum hybrids have demonstrated proof of performance and forage quality.We are working closely with AgAlumni Seed Company to commercialize DX sorghum hybrids for farmers and livestock producers.To date, we have mostly focused on developing two proof-of-concept hybrids for demonstration purposes.In the next phase of the project, we will expand these efforts into a full-blown DX sorghum breeding program to develop an array of 3-dwarf and 2-dwarf grain sorghum hybrids, sorghum x sudan hybrids, forage hybrids, and photoperiod-sensitive hybrids.We anticipate that the development of dhurrin-free sorghum cultivars has the potential to replace corn and other forage crops that have lower water-use efficiency characteristics resulting in reduced water requirements for irrigation.2.Improving sorghum seed composition and utilization:Sorghum grain protein and starch quality are key factors in determining nutritional value of sorghum; however, these traits are still poorly understood. We have approached questions of seed protein and starch quantity and quality with both forward and reverse genetics, identifying mutants by directly testing the protein digestibility in micro-porridges of flour from ground seeds (Massafarro et al 2016, Diatta et al 2019), testing properties of purified starch from these seeds (composition, structure, gelatinization, particle size) and also testing those lines that have mutations detected in genes for known starch biosynthetic enzymes and known seed storage proteins or modifiers of starch or storage proteins (Griebel et al., 2019a, 2019b).At least three mutations in genes that improve protein digestibility (Diatta et al 2019) and ten mutations in two genes influencing starch quality (Griebel et al., 2019a, 2019b) have been discovered.In the next phase of this project, we will further characterize these genes and their functions and begin to breed these alleles into food grade sorghum varieties for further testing and distribution. Products developed in the breeding pipeline will be used in proof of concept research demonstrating end-use grain and forage quality.3.Modifying sorghum plant architecture and development:Dwarfism is a useful trait in sorghum because it enables the use of mechanical harvesting and improved lodging resistance. Previous research has shown that the dw3dwarf phenotype is caused by a mutation in a P-glycoprotein (PGP) that functions as a polar auxin transporter (Multani et al., 2003). This allele has an 882 base pair tandem duplication in exon 5 that causes the protein to be non-functional (Multani et al., 2003). This allele produces an unstable phenotype with progeny of homozygous dw3plants reverting to Dw3tall-type plants at a rate of around 1/600 plants depending on the genetic background of the accession (Karper, 1932).Multani et al. (2003) showed this instability was the result of an unequal crossing over event during meiosis.A second dw3allele that produces a stable-dwarf phenotype was described by Barrero Farfan et al. (2012).This allele (dw3-sd2) was characterized by a six base pair deletion that produces a two amino acid deletion in the translated protein. The stability of this allele was demonstrated by grow-out trials of over 50,000 plants with no revertant plants observed.We hypothesized that additional stable-dwarf dw3alleles might be discovered in the standing variation of sorghum.To test this hypothesis, we conducted an analysis of the dw3gene in a large collection of sorghum conversion lines.DNA sequencing efforts revealed three additional indel alleles that should produce dwarf-stable phenotypes.To test the stability of the dwarf phenotypes represented by these alleles, the dw3allelesare being backcrossed into Tx430.Field trials will be conducted to compare the frequency of revertants in Tx430 dw3-refcompared to the four alleles. Dw3 alleles that represent a substantial improvement in stability of the dwarf phenotype will be used in parent line development for commercial uses.