Functional Study Of SsGA2ox1 And SsGA20ox1 On The Regulation Of Tallow Xylem Development

Sapium sebiferum,which belongs to the euphorbiaceous family,is an traditional oil plant in China,due to the high oil production,landscaping and pharmaceutical values.S.sebiferum has high resistance to various environmental stresses,and was widely distributed in China.The xylem is one of the most important tissues in plants,which regulated the transportation of the water,hormones and all kinds of mineral nutrients.Besides,the xylem is important for maintaining the shoot architecture.The xylem can be divided into two parts,primary xylem and secondary xylem,the later of which is the main consistence of the woods.It has been reported that gibberellin plays an important role in the regulation of plant catheter,fiber and the differentiation of the xylem.Nevertheless,the molecular mechanism how gibberellin regulated the xylem formation and differentiation still largely remains unclear.In this study,we investigated the effects of exogenous applied gibberellin and gibberellin biosynthesis inhibitor-Paclobutrazol on the xylem development,plant growth in the S.sebiferum seedlings.We also cloned and functionally characterized the molecular function of gibberellin biosynthesis and degradation-related genes,SsGA20oxl and SsGA2oxl on the xylem development in the Arabidopsis.The main results are listed as following:1.Exogenous gibberellin treatment can significantly promote the formation and differentiation of xylem in the S.sebiferum seedlings.Gibberellin not only increased the stem intemode elongation,but also promoted the xylem formation at the early growth stages in the S.sebferium seedlings.While Paclobutrazol,which was widely used as the gibberellin biosynthesis inhibitor,significantly inhibited the xylem formation.These results suggested that gibberellin played a positive role in the regulation of xylem formation and differentiation in S.sebiferum.Further,the quantitative real-time PCR showed that gibberellin could up-regulate the expression of the key genes in the regulation of lignin biosynthesis,such as Ss4CL?SsC4H?SsCCR?SsCOMT?SsFSH?SsHCT?SsPAL and SsCAD,while PAC treatment inhibited the expression of most of these genes,suggesting gibberellin regulated the xylem formation via direct regulation of the lignin biosynthesis-related genes in S.sebiferum.2.Using the stem cDNA as the template,we successfully cloned the full-length of two key genes SsGA20ox1 and SsGA2ox1,which were involved in the regulation of gibberellin biosynthesis and degradation.The results showed that overexpression of SsGA20oxl could significantly promoted the plant growth,and xylem development in the root,stem and the leaves.Overexpression of SsGA2ox1,which could lead to decreased endogenous gibberellin level,significantly retarded the plant growth and inhibited the xylem formation.These results suggested the gibberellin status which was regulated by the SsGA20ox1 and SsGA2oxl,played a central role in the regulation of Arabidopsis xylem development and differentiation.The results also showed that the xylem development-related genes,such as AtCCOAMT?AtCCR and AtCOMT were significantly up-regulated by overexpression of SsGA20ox1,while the expression of At4CL?AtC4H?AtCAD?AtCOMT?AtF5H?AtHCT and AtPAL was significantly down-regulated by overexpression of SsGA2ox1,suggesting that in Arabidopsis,the lignin biosynthesis genes were also the potential targets of gibberellin during the xylem formation and differentiation.