Identification And Expression Analysis Of MYB Transcription Factor In Latex Cells Of Hevea Brasiliensis

Rubber tree (Hevea brasiliensis ) is the primary commercial sources of natural rubber.Natural rubber is one of the secondary metabolites and stored in the laticifer cells of rubber tree. Cis-1, 4-poly isoprene is the main component of natural rubber which is synthesized by mevalonate(MVA) pathway. The general rubber biosynthetic metabolic pathway has been revealed in rubber tree, but the molecular regulation mechanism of natural rubber biosynthesis is unclear.MYB (v-MYB avian myeloblastosis viral oncogene homolog) transcription factor is one of the superfamily in higher plant, which compose of many members and play important roles, such as in primary and secondary metabolism, cell morphology, hormonal siganaling and so on. The general rubber biosynthetic metabolic pathway has been revealed in rubber tree. In this study, in order to insight of the MYB gene how to regulate the molecular mechanism on natural rubber biosynthesis, we analyzed systemically the characteristics and function of HblMYBs using the transcriptome database of the rubber tree latex and the whole genome data of rubber tree, and combined with the promoter of key enzyme of natural rubber biosynthesis.In this study, 44 MYB transcription factor genes (named HblMYB1-HblMYB44) were expressed in laticifer cells. HblMYBs are mainly made of multiple exons. The analysis of 44 HblMYB sequences showed that the highly conserved DNA domain (R unit) were found in the N-terminus, with 5 HblMYBs containing one R unit, 33 HblMYBs containing 2 R units and the other HbIMYBs containing 3 R units. Additionally, the results of the protein three-dimensional structure prediction showed that the R2 and R3 regions formed three a-helix. Phylogenetic analysis of the MYB genes between Arabidopsis and Hevea brasiliensis laticifer cells revealed that HblMYB proteins are divided into 17 subfamilies.Real-time fluorescence quantitative PCR was applied to screen out five HblMYBs(HblMYB19, HblMYB20, HblMYB25, HblMYB40 and HblMYB44), with highest expression in latex. Expression analysis of exogenous phytohormone treatments identified that five HblMYBs responded to one or more treatments. The expression of HblMYB19, HblMYB20,HblMYB40 and HblMYB44 were increased, and HblMYB25 was decreased by JA significantly. The expression of HblMYB20, HblMYB25 and HblMYB40 were increased,and HblMYB19, HblMYB44 were down-regulated by ET. The expression of HblMYB 19,HblMYB20, HblMYB25 and HblMYB40 were inhibited, and HblMYB44 was promoted by ABA. The expression of HblMYB20, HblMYB25 and HblMYB44 were reduced, and HblMYB19, HblMYB40 were not regular influence by SA treatment.The results of subcellular localization indicated that HbIMYB19, HblMYB20 and HblMYB44 were localized in the nuclears. The interaction of HbMYB44 and HbSRPP,HbFDP, HbHRT promoters was identified in yeast, which could regulated the expression of HbSRPP, HbFDP and HbHRT at the transcriptional level. A dual-luciferase assay system was employed for this study. The level of the luciferase activity controlled by HIbMYB44with HbSRPP, HbFDP and HbHRT promoters was promoted.The results suggested that HblMYB44 may be involved in the regulation of natural rubber biosynthesis,but the specific molecular mechanism remains to be further studied.