Roles of nuclear RNA binding proteins in floral reproductive morphogenesis in Arabidopsis

In Arabidopsis, a MADS-box gene AGAMOUS (AG) plays central roles in specifying reproductive organ identities and limiting the proliferation of the stem cells in the floral meristem. AG has long been the only gene with such functions until the isolation of HUA1, a zinc finger RNA binding protein, and HUA2, a putative transcriptional co-activator, from a genetic screen. In an effort to identify additional components as well as explore the functions of HUA1 and HUA2, a new enhancer screen with the hua1-1 hua2-1 mutant and a yeast two-hybrid screen using HUA2 as the bait were performed, from which at least six H&barbelow;UA ENHANCER (HEN) loci and four H&barbelow;UA2- i&barbelow;nteracting f&barbelow;actor (HIF) genes have been isolated. The roles of HUA1, HUA2, HEN4, and HIF1 (mainly HEN4 and HIF1) in floral reproductive morphogenesis have since been examined.; Strains carrying mutations in HUA1, HUA2, and HEN4 exhibit defects similar to those in ag mutants: reproductive-to-perianth organ transformation and loss of floral determinacy. Although regulation of AG was demonstrated to be primarily controlled at the transcriptional level, my studies together with others' work in the lab have begun to reveal genes that specifically facilitate the expression of AG at the post-transcriptional level. Not only HEN4, a KH domain RNA-binding protein, but also HUA1, HUA2 as well as a RNA helicase HEN2, is required for the proper processing of the pre-mRNA of AG. In addition, HUA1 is associated with HEN4 in nuclear speckles and can bind AG RNA in vitro.; HIF1, a putative splicing factor with WW domains and FF domains, was shown to be associated with HUA2 in yeast and in vitro. HIF1 is broadly expressed in plants and the protein localizes in the nucleus. Characterization of loss-of-function mutants of HIF1 and its homologous gene HFH1 suggested that, in addition to its role in floral organ fate specification, HUA2 also functions in concert with HIF1 and HFH1 to modulate floral transition and male fertility. These studies pinpoint a possible mechanism involving coupled transcription/splicing in modulating plant development.