Functional analysis of SIZ1 and LGD1 involved in rice growth and development

• Main Authors: Thangasamy Saminathan, 唐戈薩
• Other Authors: Guang-Yuh Jauh
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/81067857066956763216

博士 === 國立中興大學 === 生物科技學研究所 === 99 === Rice is a major staple food for nearly half of the world’s population and rice plant architecture including plant height, tiller number and angle, and panicle morphology is crucial for grain yield. In addition to these characteristics, the higher grain production of rice depends on successful sexual reproduction. Male sterility, caused by various defects including anther dehiscence, has adverse effects on agricultural productivity and significantly reduces the crop yield. The phenomenon of male sterility is highly exploited to produce successful hybrids with higher yield. By taking the advantage of available resources of functional genomics and T-DNA insertional mutants, functional studies of the tagged genes with important characters such as male sterility, tillering, early flowering and panicle morphology are the main foci of this dissertation. In the first part, I provided the experimental evidence for the biological function of the SUMO E3 ligase, SIZ1, in rice for anther dehiscence. In this study, we used two genetic approaches, the siz1 T-DNA mutant and SIZ1-RNAi transgenic plants, to characterize the function of rice SIZ1. Genetic results revealed co-segregation of single T-DNA insertional recessive mutation with the observed phenotypes in siz1. In addition to showing reduced plant height, tiller number, and seed set percentage, both siz1 mutant and SIZ1-RNAi transgenic plants showed obvious defects in anther dehiscence but not in pollen viability. The anther indehiscence in siz1 was due to defects in endothecium development before anthesis. Interestingly, the rice orthologs of AtIRX and ZmMADS2, which are essential for endothecium development during anther dehiscence, were significantly downregulated in siz1. Compared to the wild-type, the sumoylation profile of high molecular weight proteins in mature spikelet was significantly reduced in siz1 and SIZ1-RNAi line that showed notable reduction in SIZ1 expression. The NLS located in SIZ1 C-terminus was sufficient for its nuclear targeting in bombarded onion epidermis. All results suggest the functional role of SIZ1, a SUMO E3 ligase, in regulating rice anther dehiscence. The second part of this dissertation mainly addresses the functional characterization of an unknown gene regulating tillering and panicle development. Two genetic approaches, T-DNA insertional mutant and RNAi transgenic lines, were used to characterize its functions. Later T-DNA insertion recessive mutant was named as lagging growth and development1 (lgd1), which exhibited slow growth, reduced tillers and plant height, altered panicle architecture and grain yield. LGD1-RNAi plants showed similar phenotypes found in the lgd1. Reduced number of unelongated internodes caused few tiller numbers and semi-dwarf was due to reduced number of cells in the lgd1 mutant. LGD1, encoding a vWA domain-containing protein(s), is a single gene in rice and has ortholog in sorghum. Interestingly, 5’-RACE, GUS assay, RT-PCR and RNA blot revealed the existence of multiple transcripts and distinctive spatiotemporal expression of LGD1 transcripts. Additionally, 5’-RACE-PCR and luciferase promoter assay were used to clone multiple transcripts and to analyze different promoters of LGD1, respectively. The LGD1-GFP fusion protein is located both in the nucleus and cytoplasm. We propose that LGD1 regulates both vegetative and reproductive growth through multiple transcripts from different promoters and TSSs and the regulatory mechanism is yet to be studied. Notably, the direct downstream targets of these genes SIZ1 and LGD1 with known mechanisms will shed light on multiple phenotypes towards crop improvement through rice biotechnology.