ABSTRACT
KEY MESSAGE: The HbCZF1 protein binds to the hmg1 promoter in yeast and this interaction was confirmed in vitro. The hmg1 promoter was activated in transgenic plants by HbCZF1. Biosynthesis of natural rubber is known to be based on the mevalonate pathway in Hevea brasiliensis. The final step in the mevalonate production is catalyzed by the branch point enzyme, 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGR), which shunts HMG-CoA into the isoprenoid pathway, leading to the synthesis of natural rubber. However, molecular regulation of HMGR expression is not known. To study the transcriptional regulation of HMGR, the yeast one-hybrid experiment was performed to screen the latex cDNA library using the hmg1 (one of the three HMGR in H. brasiliensis) promoter as bait. One cDNA that encodes the CCCH-type zinc finger protein, designated as HbCZF1, was isolated from H. brasiliensis. HbCZF1 interacted with the hmg1 promoter in yeast one-hybrid system and in vitro. HbCZF1 contains a 1110 bp open reading frame that encodes 369 amino acids. The deduced HbCZF1 protein was predicted to possess a typical C-X7-C-X5-C3-H CCCH motif and RNA recognition motif. HbCZF1 was predominant in the latex, but little expression was detected in the leaves, barks, and roots. Furthermore, in transgenic tobacco plants, over-expression of HbCZF1 highly activated the hmg1 promoter. These results suggested that HbCZF1 may participate in the regulation of natural rubber biosynthesis in H. brasiliensis.