Analysis Of A Gain-of-function Mutant Sef In Arabidopsis

Maintenance of stem cell number in shoot apical meristem (SAM) is essential for the generation of later organs. WUSCHEL (WUS) is a vital component in stem cell regulatory network, which together with other stem cell regulators constitutes two feed-back loops. These two feed-back loops control homeostasis of stem cell group in SAM.In this dissertation, I analyzed a mutant sef (stem-ecotopic-flowers) obtained by screening a collection of activation tagging lines. sef showed distinct phenotype of initiating ecotopic flowers from surface of inflorescence stem and aberrant long hypocotyls of seedling. Two questions will be addressed in this dissertation: what is the mechanism of the production of ecotopic meristems on inflorescence stem, and what is the mechanism underlying the generation of long hypocotyls.Our results showed that ecotopic meristems initiated not only on inflorescence stem of sef, but also on petiole, leaf, in axils of cauline leaf, on pedicel, in axil of pedicel and on floral organs. Microscopic observation revealed that these ecotopic meristems on inflorescence stem were initiated from differentiated cortex cells. In sef, T-DNA was identified to be inserted in WUS promoter, 810 bp upstream of start code of WUS. Southern blot showed that sef was a mutant with one-copy T-DNA insertion. In order to investigate which gene was activated in sef, we checked expression level of 4 genes upstream and downstream of WUS. RT-PCR results showed that only the expression of WUS was enhanced in inflorescence stem, correlated with ecotopic flower phenotype. Not only constitutive expression of WUS but also induction of overexpression of WUS in pga6-1 with 17-b-estradiol, a WUS inducible activation tagging mutant, could phenocopied sef phenotypes. This indicated sef phenotypes were resulted from WUS overexpression. Then we carried out in situ hybridization and RT-PCR to investigate expression patterns of WUS,CLV3,LFY and AG in these...