PhD Student University of South Carolina Columbia, South Carolina
Body of Abstract: Regulation of floral organ size involves an elegant interplay among different growth regulatory modules, several of which have been identified so far. However, how the output from said modules is integrated to give rise to floral organs of characteristic sizes still remains largely unknown. The transcription factors AINTEGUMENTA (ANT) and AINTEGUMENTA-LIKE6 (AIL6) play partially redundant roles in floral organogenesis through the positioning of organ initiation, specifying organ identity, and regulating the growth of these growing organs. Our lab identified several likely direct targets of ANT and AIL6 in flowers via genomic approaches. Here, we focus on two of these identified genes that play roles in organ growth regulation- BIG BROTHER (BB), a growth repressor, and XTH9, a growth promoter. To determine the developmental stages at which ANT and AIL6 regulate the expression of BB, we have examined the spatial expression of the BB:GUS transcriptional reporter in wild-type, ant, ail6, and ant ail6 inflorescences. A yeast reporter strain containing a 1500-bp fragment corresponding to the BB promoter exhibited a 15-fold increase when transformed with ANT as compared to an empty vector, suggesting the presence of cis-regulatory elements bound by ANT. This region contains two sites with sequence similarity to the ANT consensus binding site. We will determine if ANT and AIL6 bind these DNA sequences using gel shift assays. For XTH9, we found that a 100-bp fragment corresponding to the summit of the ChIP-Seq peak upstream of XTH9 exhibited an approximately 5-fold increase in transcriptional activation when transformed with ANT. No DNA sequences with obvious similarity to the ANT consensus site are present within this fragment. Our experiments will help explicate the mechanism of ANT/AIL6 regulation of these genes, thereby adding to our current knowledge of the gene regulatory networks in floral organ growth.