Functional dissection of the promoter.

ARGONAUTES are the central effector proteins of RNA silencing which bind target transcripts in a small RNA-guided manner. has 10 () genes, with specialized roles in RNA-directed DNA methylation, post-transcriptional gene silencing, and antiviral defense. To better understand specialization among genes at the level of transcriptional regulation we tested a library of 1497 transcription factors for binding to the promoters of ,, and using yeast 1-hybrid assays. A ranked list of candidate DNA-binding TFs revealed binding of the promoter by a number of proteins in two families: the miR156-regulated SPL family and the miR319-regulated TCP family, both of which have roles in developmental timing and leaf morphology. Possible functions for SPL and TCP binding are unclear: we showed that these binding sites are not required for the polar expression pattern of , nor for the function of in leaf shape. Normal transcription levels and function appear to depend instead on an adjacent 124-bp region. Progress in understanding the structure of this promoter may aid efforts to understand how the conserved AGO7-triggered pathway functions in timing and polarity.