| The purpose of this thesis is to investigate the Arabidopsis gene SHORT INTEGUMENTS1 (SIN1) as a step towards further understanding of plant embryogenesis, meristem behavior, and flowering time control.; Prior studies showed that a recessive sin1 mutation causes pleiotropic effects in morphogenesis. The effects include, a delay in flowering time, and ovule (seed) defects. The gene was previously shown to interact with, ERECTA, a putative serin-threonine receptor kinase.; Studies reported in this thesis reveal that maternal sin1 reduction of function mutations cause embryos to develop with pattern defects. Further examinations of mutations in the SIN1 gene focused on the altered shoot apical meristem (SAM). In higher plants, the SAM produces all aerial structures. We showed that sin1 mutants produce more vegetative leaves than wild-type, and then go on to produce more lateral inflorescence branches, each step causing a delay in flowering time. Therefore, SIN1 is a positive regulator of the transition to flowering. In Arabidopsis, two genes, LEAFY and APETALA1 are required to specify floral development on the flanks of the SAM. Others have shown that loss-of-function mutations in these genes convert flowers to more inflorescence-like fates, and gain-of-function expression of either gene causes early transition to flowering. Our studies show that the sin1 mutation enhances apetala1 or leafy loss-of-function mutations. Paradoxically, sin1 mutations synergistically enhance the early flowering phenotype imparted by a gain-of-function 35S::LEAFY transgene. Conversely, sin1 mutations suppress the 35S:APETALA1 phenotype. We propose that SIN1 is an early negative post-transcriptional regulator of LEAFY.; Cloning of the putative SIN1 gene is reported here. In the process we have shown that sin1-1 is allelic to suspensor1 and that the cloned gene is interrupted in the sus1-1 allele. Analysis of the polypeptide sequence encoded by the SIN1 gene shows that it has a bipartite nuclear localization domain, two DEXH -box RNA helicase C domains, two RNase3 domains and finally two double stranded RNA binding domains. The presence of these domains supports a role for SIN1 in regulating post-transcriptional expression of developmental genes. |
