Preliminary Study On Dwarfing Mechanism Of Mutant Zs-d(Brassica Napus L.)

As an important oil crop in China,oilseed rape is prone to lodging at maturity.Lodging significantly reduced the yield and quality of rape.The lodging resistance and fertilizer tolerance of semi dwarf oilseed rape were significantly improved,and the yield was also significantly increased.Therefore,moderate reduction of plant height has become an important breeding goal of rape.In recent years,rapeseed breeders have created some dwarf oilseed rape mutants and revealed some of the molecular mechanisms of dwarf formation.Further screening and creating dwarf mutants with production and application value and studying their dwarfing mechanism will contribute to the Dwarfing breeding of oilseed rape.In this study,a semi dwarf mutant zs-d of Brassica napus derived from zhongshuang11,was used as material to explore the Dwarfing mechanism of zs-d through phenotypic identification,cytological and genetic analysis,and transcriptome sequencing,so as to lay a theoretical foundation for further revealing the molecular mechanism of zs-d dwarf formation.The main results are as follows:1.Under the condition of autumn sowing in Wuhan,Hubei Province,the height of zs-d was 42%lower than that of zhongshuang 11,the branches were more compact,the leaves were more upright,and the number of leaves increased significantly.The flowering stage of the mutant was 20.12±2.65 days later,and there was no significant difference in 1000seed weight and oil content.Under the condition of spring sowing in Badong County,Hubei Province,compared with zhongshuang 11,the plant height of zs-d decreased by50%,the height of the first branch decreased by 30%,the angle between leaves and main stem decreased,and the number of leaves increased significantly.The flowering period was 14.31±3.19 days late.2.The petiole of zs-d material is purple and the leaves are dark green,while the leaves of zhongshuang 11 are bright green.It was found that the anthocyanin extract of zs-d leaves was purplish red,while the anthocyanin extract of zhongshuang 11 was grayish green.It was found that the anthocyanin content in zs-d leaves was 4 times that of zhongshuang 11,showing a very significant difference.Compared with zhongshuang 11,the content of chlorophyll a in zs-d decreased significantly and the content of chlorophyll b increased significantly.Therefore,the value of chlorophyll a/b in zs-d leaves was less than that in zhongshuang 11 leaves.3.The plant height of 460 individual plants in F2 population was measured.It was found that the individual plant height showed continuous distribution between 20～180 cm and had the characteristics of three peak distribution.Afterc~2test,it was in line with the theoretical separation ratio of 1:2:1.It is preliminarily considered that the semi dwarf trait of zs-d is controlled by a single partial dominant gene.4.Through the observation of paraffin sections of zs-d and zhongshuang 11 stems,it was found that the length of mesocolumnar cells in zs-d decreased significantly and the proportion of small area cells increased compared with zhongshuang 11;The parenchyma cells of zs-d were narrower and longer than those of zhongshuang 11,and the number of cells increased significantly;Compared with zhongshuang 11,the area of cortical cells in zs-d decreased significantly,and the cortical cells showed a relaxed state.In cross cutting,the proportion of small area cells in zs-d was higher than that in zhongshuang 11,and the number of cells in the same area field also increased significantly;The proportion of small area parenchyma cells in zs-d was significantly higher than that in zhongshuang 11;However,the cortical cell area of zs-d was not significantly different from that of zhongshuang 11,but the cortical cells were arranged more closely.5.Transcriptome analysis of the main stems of zs-d and zhongshuang11 materials showed that 23 significantly differentially expressed genes mediating auxin signal transduction pathway were enriched by go analysis.There are six specifically expressed genes IAA16、IAA18、IAA15、IAA17、IAA28 and GH3.15,which are involved in the regulation of plant height,branch number and flowering stage.Therefore,we speculate that the phenotypes of short stem,increased number of branches and delayed flowering of zs-d may be highly correlated with it.KEGG enrichment analysis also significantly enriched hormone signal transduction pathways.A total of 84 differentially expressed genes were involved in these hormone signal transduction pathways,of which the number of auxin related differentially expressed genes was the largest(52).Therefore,we speculate that auxin related differential genes are highly correlated with the mutant phenotype of zs-d.In addition,six significantly differentially expressed genes(Bna A09G0688500ZS,Bnascaffold0027G0017600ZS,Bna A09G0135300ZS,Bna C03G0282200Z,Bna C01G0510100ZS,Bna C05G0554700ZS)were enriched in the strigolactone pathway,and all of them were down-regulated.According to previous studies,these 6 genes are involved in the regulation of plant height,branches number and anthocyanin content.Previous studies have shown that,on the one hand,strigolactone can regulate the polar transport of auxin,on the other hand,auxin can also induce the synthesis of strigolactone,and regulate plant growth and development through the interaction of these two hormones.Therefore,we speculate that the mutant phenotype of zs-d may be jointly regulated by auxin and strigolactone.