SHORT INTERNODES/STYLISH genes, regulators of auxin biosynthesis, are involved in leaf vein development in Arabidopsis thaliana.

Leaves depend on highly developed venation systems to collect fixed carbon for transport and to distribute water. We hypothesized that local regulation of auxin biosynthesis plays a role in vein development. To this effect, we assessed the role of the SHORT INTERNODES/STYLISH (SHI/STY) gene family, zinc-finger transcription factors linked to regulation of auxin biosynthesis, in Arabidopsis thaliana leaf vein development. Gene functions were assessed by a combination of high-resolution spatio-temporal expression analysis of promoter-marker lines and phenotypic analysis of plants homozygous for single and multiple mutant combinations. The SHI/STY genes showed expression patterns with variations on a common theme of activity in incipient and developing cotyledon and leaf primordia, narrowing to apices and hydathode regions. Mutant analysis of single to quintuple mutant combinations revealed dose-dependent defects in vein patterning affecting multiple vein traits, most notably in cotyledons. Here we demonstrate that local regulation of auxin biosynthesis is an important aspect of leaf vein development. Our findings also support a model in which auxin synthesized at the periphery of primordia affects vein development.

The Arabidopsis thaliana transcriptional activator STYLISH1 regulates genes affecting stamen development, cell expansion and timing of flowering.

SHORT-INTERNODES/STYLISH (SHI/STY)-family proteins redundantly regulate development of lateral organs in Arabidopsis thaliana. We have previously shown that STY1 interacts with the promoter of the auxin biosynthesis gene YUCCA (YUC)4 and activates transcription of the genes YUC4, YUC8 and OCTADECANOID-RESPONSIVE ARABIDOPSIS AP2/ERF (ORA)59 independently of protein translation. STY1 also affects auxin levels and auxin biosynthesis rates. Here we show that STY1 induces the transcription of 16 additional genes independently of protein translation. Several of these genes are tightly co-expressed with SHI/STY-family genes and/or down-regulated in SHI/STY-family multiple mutant lines, suggesting them to be regulated by SHI/STY proteins during plant development. The majority of the identified genes encode transcription factors or cell expansion-related enzymes and functional studies suggest their involvement in stamen and leaf development or flowering time regulation.