Cloning And Function Analysis Of Genes Involved In Regulation Of Early Senescence In Rice & Analysis Of QTL For Brown Rice Rate

Leaves are the primary organs required by plants to carry out photosynthesis and respiration, and they are closely related to agricultural yield. Leaf senescence in rice is one of limiting factors to develop high yield potential. An early senescence (es-n) mutant of rice (Oryza sativa L.) by mutagenesis of ethylene methylsulfonate (EMS) treatment from Nipponbare was identified and used in this study. The leaves became yellow since seeding stage, and the chlorophyll content is decreased in es-n. With the development of the leaf, it turned yellow and rusty spots were appeared, above all, leaf margin and leaf tip are both serious. In all, it shows signs of early senescence. Moreover, germination rate of es-n is decreased. And es-n has more cold tolerance compared with wild type. We performed anatomical analysis of es-n and the genetic analysis, allelic test and fine mapping through map-based cloning strategy were also be conducted. The main results were as follows:1) Genetic analysis of the phenotype of F2 segregation generation showed that ratio of wild type phenotype to early senescence in every combination is 3:1. It indicated that the character is a qualitative character controlled by a single recessive nuclear gene.2) The results of scanning electron microscope showed that, the leaf of mutant had a smoother surface than wild-type, and it lacked siliceous protuberance around the stoma; The photosynthetic efficiency, transpiration rate, stomatal conductance of es-n were less than its wild type varieties. In addition, the chloroplast in the mutant grew abnormally and there were a few starch grain in it. Paraffin section analysis showed the development of prothenchyma and vascular bundle was abnormal in the mutant.3) The ES-n gene was cloned by map-based cloning method. There was only one point mutation in the es-n. This nucleotide substitution lead to a changed splicing locus, transcription terminate advanced. Then, confirmation test was performed. There was another two early senescence mutant found, whose mutation point were different.4) The results of RT-PCR showed that the ES-n gene expressed to different extents in the different organs of the whole plants, which expressed lowly in root and leaf.5) Analysis of microarray suggested that es-n had relation with Circadian rhythm, Phenylpropanoid biosynthesis, Phenylalanine metabolism and Lysine biosynthesis Rice is one of mankind's major food staples, given continuing population growth and increasing competition for arable land between food and energy crops, food security is becoming an ever more serious global problem. Therefore, there is an urgent need to secure grain production. Pursuing high grain yield is one of the most important objectives in rice production. Many QTLs or genes for yield had been cloned and functionally characterized in recent years. Over the past decades, properties of BRR have been studied, but no consensus has been reached.In this study, a double haploid (DH) population derived from a cross between TN₁ (an indica variety) and CJ06 (a japonica variety) was used to investigate the genetic basis for milling and appearance traits. Using a constructed molecular linkage map, four QTLs for brown rice rate were detected on chromosomes 1, 8, 9, and 10. Moreover, three QTLs for appearance traits, including grain weight and grain l/w ratio, were detected on chromosomes 6, 9 and 10. Then, the q-BRR10 locus was finally located in a 149-kb DNA region between two STS markers. In order to clone the BRR gene, we established chromosome segment substitution lines at the q-BRR10 locus. Results from the Paraffin sections suggest that the number of hull sclerenchyma cells layers may be the key factors for brown rice rate.The genetic bases of BRR, qGL/W-6, GW9 and GW10 have received much attention because of their importance in rice yield. Results from this study can be useful in many ways for improving the milling quality as well as grain yield: to increase grain weight, to decrease hull weight, in other words, to increase brown rice rate, not to affect the yield. The closely linked markers that flank the QTLs identified should be very useful when transferring genes in breeding programs. Moreover, this study was also benefit to research seed development.