Gene Cluster Responsible for Validamycin Biosynthesis in Streptomyces hygroscopicus subsp. jinggangensis 5008

Abstract

ABSTRACT A gene cluster responsible for the biosynthesis of validamycin, an aminocyclitol antibiotic widely used as a control agent for sheath blight disease of rice plants, was identified from Streptomyces hygroscopicus subsp. jinggangensis 5008 using heterologous probe acbC , a gene involved in the cyclization of d -sedoheptulose 7-phosphate to 2- epi -5- epi -valiolone of the acarbose biosynthetic gene cluster originated from Actinoplanes sp. strain SE50/110. Deletion of a 30-kb DNA fragment from this cluster in the chromosome resulted in loss of validamycin production, confirming a direct involvement of the gene cluster in the biosynthesis of this important plant protectant. A sequenced 6-kb fragment contained valA (an acbC homologue encoding a putative cyclase) as well as two additional complete open reading frames ( valB and valC , encoding a putative adenyltransferase and a kinase, respectively), which are organized as an operon. The function of ValA was genetically demonstrated to be essential for validamycin production and biochemically shown to be responsible specifically for the cyclization of d -sedoheptulose 7-phosphate to 2- epi -5- epi -valiolone in vitro using the ValA protein heterologously overexpressed in E. coli . The information obtained should pave the way for further detailed analysis of the complete biosynthetic pathway, which would lead to a complete understanding of validamycin biosynthesis.