Meristem Identity Genes and the Evolution of Plant Architecture in Brassicaceae

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0234118BaumThe development of plants is controlled by meristems, areas of organized cell division and differentiation. Shoot meristems can take on either a floral or vegetative identity depending upon the activity of a set of meristem identity genes. Because flowers terminate shoot growth, the distribution of flowers, and hence the regulation of meristem identity genes, may have a profound affect upon plant architecture. Thus, it has been hypothesized that the architectural differences between species are largely driven by changes in meristem identity genes. In the proposed work we will evaluate the role of three meristem identity genes, LFY, TFL1, and AP1, in explaining why three species of the mustard/cabbage family (Brassicaceae) produce flowers from the basal rosette of leaves rather than on an elongated leafless stem (the inflorescence).In previous work the PI studied LFY genes from three rosette flowering species, Ionopsidium acaule (Ia), Idahoa scapigera (Is), and Leavenworthia crassa (Lc). They used transformation to introduce LFY genes from these three species into plants of an inflorescence flowering species, Arabidopsis thaliana (that lacked a functional endogenous copy of LFY). They found that whereas Ia-LFY had no affect on plant architecture, the IsLFY and LcLFY genes tended to induce modifications to plant architecture reminiscent of rosette flowering, but they did not cause complete conversion to rosette flowering. This result suggests that evolutionary changes at the LFY locus contributed to the parallel evolution of rosette flowering in these species, but point to additional, as yet unidentified, genetic changes. The proposed work will include follow-up experiments on LFY aimed at determining whether the important differences between species are located in the protein-coding region or the adjacent regulatory DNA. Similar experiments with AP1 and TFL1 will be done to see if they may have contributed to the evolution of rosette flowering. Specifically, the goal is to clarify the molecular evolution of the genes and move them from the rosette flowering species into A. thaliana to see if they can induce rosette-flowering individually or jointly with the exogenous LFY genes.This proposed study will shed light on how evolutionary changes in DNA translate into difference in the morphology of living species. In particular, the work will clarify: (1) the extent to which genetic changes are concentrated in a small set of developmental genes, (2) the relative importance of protein versus regulatory changes, and (3) the extent to which parallel evolution in independent lineages uses the same genetic toolbox. Additionally, the specific understanding of how plant architecture is regulated could ultimately have significance for efforts to modify crop plants to facilitate higher productivity and easier harvesting.The research will contribute to the training of one graduate student and one postdoctoral scientist.