Sequencing Medicago truncatula chromosome 4, expression profiling and genomic organization of NBS-LRR genes.

摘要

Our laboratory, as a member of the International Consortium was sequencing chromosomes 1, 4, 6 and 8 of the model legume, Medicago truncatula. Overall 75% of the euchromatic region is sequenced and encodes approximately 53,000 protein coding genes.;I focused my research on sequencing chromosome 4 and studying the genomic organization and expression profiles of Nucleotide Binding Sites and Leucine Rich Repeat (NBS-LRR) genes encoded on them. Chromosome 4 is one of the largest chromosomes and is distinctly divided in to a gene rich euchromatic region and a repeat rich heterochromatin. Other chromosomes have high synteny blocks with both monocots and dicots except chromosome 4 and 6 that have lower synteny with monocots. NBS-LRR genes are the largest superfamily of plant resistance genes and I have identified 447 NBS-LRR genes in the overall genome. Chromosomes 4 and 6 encodes most of the TNL genes while a large portion of the CNL type genes are mapped to chromosome 3, 5 and 8. In Medicago, NBS-LRR genes have a high degree of clustering, mainly due to local/tandem duplication, with some evidence of ectopic translocation, fusion and/or truncation that leads to an unusual high number of domain rearrangements suggesting that they evolved by duplication, although their occurrence on two chromosomes that they likely occurred after polyploidy. In addition, the expression profile of the NBS-LRR reveals that since these genes are expressed in various tissues as well as during plant symbiosis, abiotic stress and different developmental stages, that they likely are involved in functions other than just plant defense.;This study has helped in understanding the organization and the evolution of NBS-LRR genes and their expression pattern via in-silico methods. With the help of this analysis and an in-depth study of the NBS-LRR genes at molecular level, will enable us to understand their mechanism in performing the various functions.