[Cloning, sequencing and expression of Sinorhizobium meliloti strain 042B gene nodD]

S. meliloti strain 042B is a rhizobium strain which can form nodules both on alfalfa and on soybean. In this study, nodD gene of 042B was cloned into pBBR1MCS-5. By functional analysis in the system of R. leguminosarum bv. viciae LPR5045 (pSym-, pMP154), it was found that the NodD has responses both to luteolin and to genistein. This result showed that the 042B nodD gene is probably a specific nodulation determinant which determined its capability of nodulation on both alfalfa and soybean. The nodD fragment was then cloned into the expressional vector pThioHis A, B and C, and three recombinant plasmids pXDA, pXDB and pXDC were constructed. The plasmid pXDC was identified to be in the same open reading frame with the trxA gene of pThioHis C throuth sequencing analysis. Inducing IPTG and analyzing with SDS-PAGE, it was found that the fusion protein expressed from E. coli Top10(pXDC) with the molecular weight of TrXA and NodD together. The Western bolt result demonstrated that the expression result is the target gene nodD product.