| As a model species of monocotyledonous plants,the research in rice has become a hot spot in traditional breeding and molecular biology field.In practice,universal phenomenon of sheathed panicle appears in the sterile lines of hybrid rice,resulting a serious impact on hybrid rice seed-production.Cloning mutated gene causative this phenotype and identifing the molecular biological mechanism underlying sheathed panicle formation will beneficial on reducing seed-production costs and improving hybrid yield and quality.At present study,we reported a preliminary study on a sheathed panicle mutant,sui2.After phenotypic analysis and cytological observation,we then conducted map-based gene cloning,transgenic verification,as well as transcription level assess to BR-related gene.The main results are as follows:1.Phenotypic analysis showed that the panicle was wrapped by the flag leaf sheath in sui2,the uppermost internode and penultimate internode shortened respectively,especially the uppermost internode.In addition,sui2 displayed dwarfism,increased number of tillers,decreased number of grain per panicles and seed setting rate,added to larger grains,narrower flag leaves,and significantly enlarged the angle between the last and penultimate leaf.The shortening of the uppermost internode in sui2 is the main reason for the dwarfing of plants.2.The parenchyma cells of uppermost internode from cross-sectional or longitudinal sections were counted with PI staining method,and found that comparing with the wild type,the cell number were insignificantly different from those of the sui2,however,the size of parenchyma cells were smaller,suggesting that the sheathed panicle phenotype of sui2 are caused by the blockage of cell elongation.Thickened stem wall,significantly reduced air medullary cavity and decreased number of vascular bundles were also observed.3.The genetic analysis showed that the trait of sheathed panicle was decided by a pair of dominant gene.Then,the candidate gene SUI2 was mapped in the interval of 110 Kb flanked by the markers of S4-14.1 and S4-14.2 on chromosome 4.Sequencing the genome of all 14 putative genes on the region showed no base pair variation,indicating the phenotype of sui2 was not directly caused by any alternation in DNA sequence.Through quantitative analysis,the expression level of LOC?Os04g39430 in sui2 was significantly higher than that of wild type.The expression level of SUI2 in young panicles,leaf pulvini,and culms of sui2 was significantly increased by more than 200 times.The expression level of SUI2 increased by 514 times,369 times and 214 times in young panicles,leaf pulvini and culms respectively.One an D11 allellic gene LOC?Os04g39430,encoding a cytochrome P450 protein,was supposed to be the candidate gene involved in the regulation of rice panicle phenotype,which was verified through the phenotypic similarity to sui2 from transgenic plants overexpressed SUI2 to japonica variety Kitaake.4.Analysis of expression levels of brassinolide synthesis and signaling related genes in culms revealed that,compared with the wild type,the expression levels in three synthetic genes did not change uniform Ly,and the expression level in four out of six signaling related genes significantly up-regulated nearly 5 times,especially the gene BU1,indicating that some genes of the BR signal pathway participated in the regulation of the internode elongation.These results would beneficial on further research how BR signaling-related genes modulate on uppermost internode elongation. |
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