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Abstract

Flowering of the reference plant Arabidopsis thaliana is controlled by several signaling pathways that converge on a small set of genes that function as pathway integrators. We have analyzed the genomic response to one type of floral inductive signal, photoperiod, to dissect the function of several genes transducing this stimulus. We found two groups of transcription factor genes, one encoding AP2 domains and the other SBP domains, that are repressed and induced, respectively, in response to the CONSTANS/FT signaling cascade, which is activated by changes in photoperiod. The two groups are targets of the miR172 and miR156 microRNA families, and I will present data on the consequen- ces of manipulating miR172 and miR156 levels in plants. We have also studied in detail the role of microRNAs in a different developmental process, leaf growth. In a genetic screen, we identified the JAW locus, which produces a microRNA that can guide mRNA cleavage of several TCP genes controlling leaf development. We found that microRNA-guided cleavage of TCP4 mRNA is necessary to prevent aberrant activity of the TCP4 gene expressed from its native promoter. In addition, overexpression of wild-type and microRNA-resistant TCP variants demonstrates that mRNA cleavage is largely sufficient to restrict TCP function to its normal domain of activity. These studies were the first linking a plant microRNA to a specific developmental process.