Progress 01/15/10 to 01/14/13
Outputs
Target Audience: The target audience was other scientists in ARS and Universities, and scientists in other countries. The target audience also includes breeders working with cereal crops. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? Trained one U.C. Berkeley undergraduate, Thant Naing. Collaboration with Dr. James Kronstad, University of British Columbia on the analysis of miR156 and miR172 expression and their targets in monocots infected by Ustilago maydis. Collaboration with Dr. Burkhard Schulz, Purdue University on the analysis Brassinosteroid biosynthesis in maize. Collaboration with Dr. Yuval Eshed of the Weismann Institute of Science to produce a sequenced based atlas of plant development How have the results been disseminated to communities of interest? through posters and talks. These were listed in products. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Objective 1. Examine the response of the miR172 gene family and its targets to GA. Through our analysis of the miR156 over-expresser Corngrass1 (Cg1), we found that the converse reciprocal expression pattern between miR156 and miR172 is mediated by GA. The expression of miR172 in GA mutant backgrounds, and in mutants rescued with exogenous GA was assayed by microRNA northern blots. miR172 expression was found to be reduced in GA deficient mutants, but restored to normal levels upon rescue with GA spray. This same pattern was also seen with the brassinosteroid mutant nana1, indicating that several hormone networks may converge to regulate miR172 expression. This GA rescue, however, was not observed in Cg1 mutants. These results are explained by recently published data from Arabidopsis where it was found that targets of miR156 are repressed by the GA regulated DELLA proteins (Yu et al. Plant Cell 2012 24 (8): 3320-32). Upon exposure to GA, DELLAs are degraded and miR156 targets become active to directly regulate the expression of miR172. Thus, the positive GA effect on miR172 and its targets is an indirect result of miR156 target gene repression by GA. Objective 2. Determine the functions of the target genes of miR172. Loss of function transposon knockout mutants have now been isolated into five of the six known AP2 target genes of miR172. These knockouts include the previously described glossy15 mutant that controls juvenile to adult phase change as well as the indeterminate spikelet1 and sister of indeterminate spikelet genes described by our group that control spikelet meristem identity (Chuck et al. Development 2008 135(18) 3013-9). In addition to these genes, we have recently isolated knockouts into a pair of duplicated target genes named zmlipless1 and sister of zmlipless1, that together appear to play roles in the specification of outer whorl floral organ identity, including the lodicules. Data from barley indicates that these genes are also responsible for cleistogamous florets (Nair et al. PNAS 2010, 107(1): 490-5). In light of the fact that other miR172 targets such as the wheat Q gene are domestication loci, these results indicate that the miR172 regulated AP2 genes are agronomically important. Objective 3. Identify downstream genes that are directly regulated by select AP2 target genes. Antibodies have been made to the AP2 gene indeterminate spikelet1 in order to perform chromatin immunoprecipitation and deep sequencing to facilitate identification of downstream genes. These experiments are in progress. Objective 4. Determine the effects of altering expression of miR172 or its targets. Constructs overexpressing miR172 behind different tissue specific promoters have been made and tested in Arabidopsis. Arabidopsis transformants expressing miR172 behind the seed specific NAPIN promoter show an increase in seed size, indicating that AP2 genes may be involved in limited seed growth. We are currently testing this hypothesis in agronomically important grass crops such as Setaria Italica.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2011
Citation:
Hartwig T, Chuck GS, Fujioka S, Klempien A, Weizbauer R, Potluri DP, Choe S, Johal GS, Schulz B.
Proc Natl Acad Sci U S A. 2011 Dec 6;108(49):19814-9. Epub 2011 Nov 21.
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