MYB transcription factors hold vital roles in the regulation of plant secondary metabolic pathways. Laticifers in rubber trees (Hevea brasiliensis) are of primary importance in natural rubber production because natural rubber is formed and stored within these structures. To understand the role of MYB transcription factors in the specialized cells, we identified 44 MYB genes (named HblMYB1 to HblMYB44) by using our previously obtained transcriptome database of rubber tree laticifer cells and the public rubber tree genome database. Expression profiles showed that five MYB genes were highly expressed in the laticifers. HblMYB19 and HblMYB44 were selected for further study. HblMYB19 and HblMYB44 bound the promoters of HbFDPS1, HbSRPP, and HRT1 in yeast. Furthermore, the transient overexpression of HblMYB19 and HblMYB44 in tobacco plants significantly increased the activity of the promoters of HbFDPS1, HbSRPP, and HRT1. Basing on this information, we proposed that HblMYB19 and HblMYB44 are the regulators of HbFDPS1, HbSRPP, and HRT1, which are involved in the biosynthesis pathway of natural rubber.

MADS-box transcription factors possess many functions in plant reproduction and development. However, few MADS-box genes related to secondary metabolites regulation have been identified. In H evea brasiliensis , natural rubber is a representative cis -polyisoprenoids in secondary metabolism which occurs in the rubber laticifer cells, the molecular regulation basis of natural rubber biosynthesis is not clear. Here, a total of 24 MADS-box genes including 4 type I MADS-box genes and 20 type II MADS-box genes were identified in the transcriptome of rubber tree latex. The phylogenetic analysis was performed to clarify the evolutionary relationships of all the 24 rubber tree MADS-box proteins with MADS-box transcription factors from Arabidopsis thaliana and Oryza sativa . Four type I MADS-box genes were subdivided into Mα (3 genes) and Mβ (1 gene). Twenty type II MADS-box genes were subclassified into MIKC* (8 genes) and MIKC c (12 genes). Eight MADS-box genes ( HblMADS3 , 5 , 6 , 7 , 9 , 13 , 23 , 24 ) were predominant expression in laticifers. ABA up-regulated the expression of HblMADS9 , and the expression of HblMADS3 , HblMADS5 , HblMADS24 were up-regulated by MeJA. The function of HblMADS24 was elucidated. HblMADS24 bound HbFPS1 promoter in yeast and HblMADS24 activated HbFPS1 promoter in tobacco plants. Moreover, we proposed that HblMADS24 is a transcription activator of HbFPS1 which taking part in natural rubber biosynthesis.