Gene Expression Analysis Of ABA/GA Pathway And Their Impact On Vivipary Process In Kandelia Obovata

In order to understand the molecular mechanism of mangroves plants,Kandelia obovata is used as the research material in this study,and four key periods,including ovule,linear embryo,closed testa and opened testa,are selected.In addition,the fruit is divided into three major tissue groups:embryo,testa and pericarp,for the differential analysis of the temporal-spatial gene expression.The transcriptome sequencing data of five tissues in S2-linear embryo and S3-closed testa are analyzed,and six groups are settled for comparison.The KEGG pathway enrichment results of differentially expressed genes indicate that:Flavonoids and other resistance compound accumulate gradually within the embryo and testa,which improve the abilibity of Kobovata seed to resistant environmental stresses;Photosynthesis in linear embryos suggest that though embryo is surrounded by testa,it can still accumulate energy and promote their growth by photosynthesis;The mainly pathway for the enrichment of differentially expressed genes is plant hormone signal transduction,including the hormonal response of ABA and GA.In addition,there is a down regulation of ABA synthesis pathway gene expression in the development of embryo.As the ABA/GA ratio plays an important role in the transition from seed dormancy to germination,and based on the evidences of most viviparous mutants are ABA-insensitive or ABA-deficient,it believes that the vivipary process of Kobovata is regulated by this two antagonistic hormones together.Therefore,14 genes related to ABA/GA metabolic pathways are selected in this study.For ABA pathway,including ABA synthesis:KoAA1,KoNCED,KoABA2,KoAA03;ABA degradation:KoCYP707A;ABA response:KoPYL9,KoSnRK2.2,KoABI3,KoABI5,KoCHO1.For GA pathway,including GA synthesis:KoKS,KoKAO;GA degradation:KoGA2ox;GA response:KoGID1.The quantitative real time PCR is used to confirm the expression pattern of these genes,and then combine their roles in the ABA/GA pathways,the results show:(1)ABA synthesis of non-viviparous and viviparous seeds is in similar pattern.The initial stage of ABA synthesis only occurs in embryos,but the final synthesis sites are embryo and testa,and the synthesis of ABA declines along with the development of embryos.(2)The time point of ABA degradation of viviparous "seeds" is different from that of non-viviparous seeds.ABA degradation is suppressed in non-viviparous seeds,while ABA degradation gene CYP707A expresses in a high expression level in viviparous seeds,especially in testa.It maintains the ABA content at a low level in the seed of Kobovata.(3)The active sites of GA are axis and testa,which coordinates the continuous growth of the axis of Kobovata by promoting the growth potential of embryo axis and loosing cell wall of testa.(4)Low concentration of ABA leads to a decrease in the ratio of ABA/GA.The dynamic balance and interaction of these two hormones constitute a common regulatory network,which may be the main reason for the continuous growth of K.obovata embryo.In this research,the transcriptome data of different developmental stages and tissues of K.obovata is analyzed,and it is concluded that ABA/GA is an important regulatory factor in K.obovata embryonic development process.Based on this,synthesis,degradation and response gene expression patterns of ABA/GA are sutdied,and the ABA/GA gene expression spatial-temporal regulation network is built.From the developmental stage specificity and tissue specificity,it is clarified how ABA/GA regulates the development of K.obovata embryos,which helps the further research on the understanding of the molecular mechanism of the vivipary process of mangrove plants.