The minimal pSymA symbiotic nitrogen fixation gene region of Sinorhizobium meliloti
Jiarui Huang, Zahed Muhammed, George C. diCenzo, Maryam Zamani, and Turlough M. Finan. Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1
Sinorhizobium meliloti is a model bacterium for the study of symbiotic nitrogen fixation (SNF). It infects the roots of alfalfa as well as some other legumes and differentiates into N2-fixing bacteroids within the plant cells of specialized nodule organs. To understand the genes essential for SNF and, in the longer term, to facilitate the manipulation of this SNF process for agricultural purposes, it is highly desirable to construct the minimal genome for SNF in this organism. S. meliloti harbors two replicons essential for SNF: a 1.7-Mb chromid (pSymB) and a 1.4-Mb megaplasmid (pSymA). A previous deletion analysis identified that only four loci, accounting for <12% of the total sequences of pSymA and pSymB, were essential for SNF, and each replicon contained two SNF-essential regions. The two SNF-essential regions in pSymA are ~103 kb (402136 ~ 505335 nt) and ~52 kb (624863 ~ 677157 nt), respectively. Here we report progress towards the cloning of these two SNF-essential regions on a plasmid in Escherichia coli, and the integration of this plasmid into the genome of a ∆pSymA S. meliloti derivative strain. We are testing the SNF ability of this strain on alfalfa to determine if the SNF-essential regions from pSymA are sufficient to restore the symbiotic capabilities to the ∆pSymA derivative strain with alfalfa.