Minisymposium 20: Photomorphogenesis

Abs # 41003: Differential roles of the Arabidopsis FRS gene family members in regulating light and phytohormone signal transduction

Presenter:	Wang, Haiyang
Authors	Lin, Rongcheng  (A)   Yang, Jianping  (A)   Wang, Haiyang  (A)
Affiliations:	(A): Boyce Thompson Institute

FHY3 and FAR1 are two homologous proteins essential for phytochrome A controlled far-red responses in Arabidopsis. There are twelve additional FHY3/FAR1-related genes (named FRS, for FAR1-related sequences) in the Arabidopsis genome. This family of proteins is evolutionarily conserved, but appears to be plant-specific. Their amino acid sequence similarity and conserved secondary structure (most FRS proteins contain 1-3 coiled-coil domains and a putative nuclear localization signal) suggest that this family of proteins may function in various signal transduction processes. To understand their roles in Arabidopsis development, we first assessed their gene expression patterns. Semi-quantitative RT-PCR analyses revealed that all FRS genes except FRS10 are expressed in all tissues examined, including rosette leaves, cauline leaves, inflorescence stems, flowers and siliques. Further, gene specific promoter::GUS fusion reporter lines were generated for each of the FRS genes. Preliminary studies employing these reporter gene lines revealed that all these FRS genes except FRS1 are clearly expressed in hypocotyls. Comparison of dark- versus far-red light-grown seedlings showed that a number of them are induced by far-red light (such as FRS3, FRS6, FRS7 and FRS9). These results are consistent with a role of these genes in regulating light control of Arabidopsis development. Secondly, we determined their protein subcellular localizations in onion epidermal cells through transient expression of their translational fusions with green fluorescent protein (GFP). It was found that these FRS proteins with predicted nuclear localization signal are indeed targeted into nucleus, suggesting that they are likely involved in regulating nuclear gene expression (such as FRS2, FRS6, FRS11 and FRS12). Thirdly, we are generating both loss-of-function (RNAi and knockout mutants) and gain-of-function mutants (via constitutive overexpression) for each of the FRS gene family members. In addition, we are generating various double and higher order mutant combinations to overcome potential functional redundancy among family members. Our preliminary studies with available mutants indicated that these proteins play important roles in mediating various light- and phytohormone-mediated responses. Progress on functional analysis of this gene family in regulating Arabidopsis development will be presented at the meeting.