The full-length annexin gene,MtAnn3,of Medicago truncatula was cloned by 5' RACE.Compared with typical annexins,which contain a head domain and four homologous repeats in the conserved core domain,the MtAnn3 protein has only one repeat in the core domain.MtAnn3 can bind cell membranes when transiently expressed in onion epidermal cells.Agrobacterium rhizogenes-mediated transformation of MtAnn3 into Medicago roots revealed that overexpression of the gene can change the polarity of root hair growth in Ca2+-free medium.The plant hormone cytokinin was able to upregulate the expression of MtAnn3.While MtAnn3 transcripts were detected in young nodules,expression was not nodule-specific,and could be detected at high levels in the roots,stems and leaves as well.
GONG ZiYingSONG XueCHEN GongYouZHU JiaBiYU GuanQiaoZOU HuaSong
Our previous work showed that an enoyl-ACP reductase gene fabI1 of Sinorhizobium meliloti was down-regulated in the nifA mutant nodule bacteria. To gain a better understanding of fabI1 gene, a single site insertion mutant was constructed in this study. The fabI1 mutant was retarded in cell growth, and its ability to grow on media with high concentration of NaCl was reduced. In addition, the mutant was completely defective in swarming phenotype. During symbiosis, the fabI1 mutant had delayed nodule formation on host plants. Despite the fact that FabI1 protein showed 66% identity with another enoyl-ACP reductase FabI2 in S. meliloti, defects in fabI1 were not rescued by the plasmidborne version of fabI2. This indicated the different functions of the two FabI proteins in S. meliloti.
