Functional Identification Of Lignin Biosyntheses Related MYB Genes From H. Brasiliensis

This paper analyzes the deposition regular pattern of lignin of Hevea brasiliensis buds and as Arabidopsis thaliana lignin synthesis regulation and related to MYB for designing probe. It will screen clones from Transcriptome, getting Seven H. brasiliensis HbMYB genes which may be involved in lignin synthesis. On this basis, it appraises function on the expression pattern analysis of H. brasiliensis and roles in A. thaliana were also studied. This work aimed to reveal the important function of HbMYB for regulating lignin biosynthesis and secondary cell wall formation in this species, and also provide theoretical basis for the genetic improvement of the wood formation in H. brasiliensis.1. The accumulation and content analysis of lignin of H. brasiliensis buds showed that the deposition and content increasing of lignin in the growth process, A large increase from terminal buds to inter whorl2, which conform to the rule of trees bud lignin accumulation. There are differences between different varieties lignin content, which may be one of the causes of different varieties of wind resistance.2. Here, using probe of A.thaliana MYB related lignin synthesis, screening from transcriptome, MYB transcription factors genes designated HbMYB85a/b, HbMYB103a/b, HbMYB52l/s and HbMYB20from H. brasiliensis. Domain analysis showed that HbMYB genes contain two characteristic MYB domains, indicate that all the seven HbMYB are R2R3-MYB ranscription factor gene. The analysis of homologous and evolution showed that, HbMYB85a/b and HbMYB20belonged to G8subgroup member of lignin synthesis, which had high identity to AtMYB20/43and AtMYB85/42; HbMYB103a/b belonged to G30subgroup member of lignin synthesis, which had high identity to AtMYB103; HbMYB521/s belonged to G21subgroup member of lignin synthesis, which had high identity to AtMYB52. All the seven genes belong lignin and secondary cell wall synthesis and development related R2R3-MYB transcription factors.3. The gene expressions suggested the all seven MYB transcription factor were higher expression in stems than xylem, but less in leaf of H.brasiliensis. HbMYB have different expressed in different varieties, showed that temporal and spatial expression of all the seven genes in H.brasiliensis. for another,The expression of different MYB gene in the same species of H.brasiliensis are also different, indicating that Although all the seven genes are associated with lignin biosynthesis, but each has its own unique features of expression.4. The genes were investigated through transform to A. thaliana. the results showed that:the over-expression of HbMYB20in A. thaliana have led to dwarfism in the transgenic plants, a significant thinning in vessels and fiber cell wall, an obvious decrease in lignin contents. The expression inhibition of the genes related to lignin and cellulose biosynthesis were found. Thus, it is reasonable to infer that HbMYB20plays a negative roles in lignin and cellulose biosyntheses, would be a negative regulation factor of secondary wall development in H. brasiliensis; the over-expression of HbMYB85a/b inA. thaliana have led to lignin content increased in the transgenic plants, a significant increasing the thickness in vessels and fiber cell wall, an obvious increased expression of lignin biosynthesis enzymes; The transgenic HbMYB103a/b A. thaliana Showed growth retardation, increase the proportion of secondary cells, ectopic deposition of lignin, and increased expression of lignin synthesis enzymes, it is confident to infer that HbMYB85a/b and HbMYB103a/b were considered as positive transcription factor of secondary growth and lignin synthesis in H. brasiliensis; the over-expression of HbMYB52l in A. thaliana have led to inhibition of growth, including small plant and partial of the plant can complete the normal growth and development, and cell wall thickening of the interfascicular fiber,but reduced numbers of vessel, circumstantial evidence suggests HbMYB52l not only involved regulation of secondary wall growth, but regulated other metabolic development process in the plant; the emergence of lines of different phenotypes indicated HbMYB52s may be due different insertion loci, so that we need further study function of this gene.