February 13 2006
9:30 LSB 2320

Abstract:

In the developing leaf primoridium of Arabidopsis, differences in gene activity along the radial axis signal morphogenesis and differentiation into the top (adaxial) and bottom (abaxial) portions of the leaf blade. Genetic and molecular studies have shown that microRNAs are key regulators of gene activity in the developing leaf. MicroRNAs (miRNAs) are ~22-nucleotide noncoding RNAs that negatively regulate gene expression via complementary sequences in target mRNAs, directing mRNA degradation or inhibiting productive translation. MicroRNA regulation of the HD-ZIP III transcription factors, PHABULOSA (PHB) and PHAVOLUTA (PHV), is required to limit PHB and PHV activity to the adaxial domain of the leaf. Gain-of-function mutations of PHB and PHV which disrupt miRNA regulation radialize the leaf blade. Abaxial fate determinants are also likely to be targeted by small regulatory RNAs. Therefore, miRNAs may help maintain a balance between cell fates in the developing leaf primordium to influence organ shape.