ISOLATION OF GENES FOR SALT TOLERANCE FROM SINORHIZOBIUMLT 11

摘要

Almost 40% of area over the world cannot be cultivated because of salinity problems. Salinity does reduce water available for plant growth resulting in decreased productivity of most crop plants. Some of leguminous plants can tolerate up to 0.1 M saltwhile Rhizobium strain that nodulate them are generally sensitive to salt. We have identified a Sinorhizobium strain LT11 from Thailand, which can tolerate up to 0.4 M salt and is effective in N2 fixation. The objective of this work was to isolate genesfor salt tolerance from this strain. The genomic DNA library of LT11 was transferred by conjugation to salt-sensitive rhizobial strain TALI 145 and the transconjugants were selected on YEM agar containing 0.1 M NaCl. Two hundred colonies that grew undersalt were isolated and the recombinant cosmid clones were isolated from twenty-one of those colonies. These cosmid clones were classified into two groups after digestion with HincKIII (Fig. 1). The analysis of sequence at the end of each fragments revealed interesting results. The first group of clones showed a relatively high homology with betaine aldehyde dehydrogenase cluster (betA and betB gene) of S. meliloti. The second group exhibited similarity with methylase, xanthine dehydrogenase, transcriptional regulator syrB (AraC family) and a conserved hypothetical protein (Fig. 2). These two groups of clones were introduced into Bradyrhizobium japonicum THA6 and the growth of the resulting strains was checked under different salt condition. Transconjugants showed better growth than THA6 wild type (Fig. 3).