Collaborative Research: Genetic Comparisons of Abscission Zones in Grasses

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At the dawn of agriculture, our ancestors harvested wild grains and began replanting them year after year. This process rapidly led to selection for grains that stayed on the plant, instead of falling on the ground. Now, 10,000 years later, this capacity to stay on the plant until harvest has obvious economic importance. The change from wild grains that fall and cultivated ones that do not is caused by naturally occurring mutations in a normal (that is wild) process. However, the process of shedding seeds occurs differently in different grains. For example, the details of dropping seeds in wild rice are different from those in wild sorghum or wild millet. This project will discover what natural mutations led to the cultivated grains, and whether the natural process of shedding seeds in rice, sorghum, and millet is genetically similar. Because retaining seeds on the plant is the very basis of agriculture, it is an obvious aspect of plants that can engage students at all education levels. Master teachers and undergraduate education majors at Oklahoma State University, as well as undergraduate science majors and local high school students, will participate actively in the observations and data collection required for the project.Shedding of seeds occurs via a characteristic zone of weakness, the abscission zone (AZ), in which the contents of cells and cell walls are modified to allow a fruit to fall off the parent plant. This project will test whether development is generally conservative, i.e., whether the AZ is produced by activating a conserved developmental program at different times or in different locations, or whether development produces novel structures (in this case, the AZ) by using novel gene combinations. Specifically, recombinant inbred lines and wild accessions will be used to identify genes that contribute to shattering in the model species green millet (Setaria viridis). These studies will be complemented by transcriptomic data on green millet in comparison to Brachypodium distachyon and rice. These investigations will test the hypothesis that some aspects of AZ development are shared among the three species but that many aspects differ because the AZ forms in a different position in each. The investigation will then be expanded to many other grasses, some of which are similar to millet, rice and Brachypodium, and some of which show distinct patterns of seed shedding. The results will define the extent of parallel and convergent evolution in an ecologically and economically critical pathway.