Comparative Mitochondrial Genome Analysis Of Brassica And MSH1-mediating Leaf Senescence

We employed comparative mitochondrial genome analysis, genome recombination and MSH1-mediating leaf senescence to analyze the evolution of the allopolyploid in Brassica and MSH1-mediateing growth traits in Brassica.1) B. juncea and B. nigra mitochondrial main circle genomes with 219919 bp (Genbank accession:KJ461445) and 232,407 bp (Genbank accession:KP030753) were generated through de novo assembly. Through annotation,34 protein coding genes,3 rRNA genes,20 tRNA genes,45 ORFs and a 2427 bp large repeat were detected in B. juncea while 33 protein coding genes,3 rRNA genes,19 tRNA genes, 41 ORFs and a 6547 bp large repeat in B. nigra.2) The synteny analysis of 6 mitochondrial genomes in Brassica was carried. The result was that the three diploid species, B. rapa, B. nigra and B. oleracea, have good linearity with their corresponding allotetraploid species, B. juncea, B. carinata and B. napus, respectively. They were divided the 11 Brassica genotypes into three groups based on Principal component analysis (PCA). B. nigra and B. carinata were clustered in one group that represents the B genome in Brassica. The botrytis-type B. oleracea and the napus-type B. napus were clustered into another group representing the C genome in Brassica. The remaining seven genotypes, including all three B. juncea, two B. oleracea, one B. napus and one B. rapa were clustered into the third group, which is a mixed group but the majority represent the A genome in Brassica.Also, the phylogenetic analysis got the same result. The divergence times based on mitochondrial genomes are consistent with the values calculated using the nuclear genomes in Brassica species, which had been reported. Furthermore,11 mitochondrial genome sequences were analysed concerning repeated sequences, coding regions and rearrangement. A similar number of repeated sequences and coding region genes were founded in species who have close phylogenetic relationship.3) MSH1 is the key gene involved in regulation of mitochondrial genome recombination and chloroplast development. This study explores the MSH1-mediating leaf senescence. The results indicated that leaf senescence leads to the down-regulation of MSH1 gene, but no obvious mitochondrial genome recombination was detected. MSH1-RNAi plants showed delayed leaf senescence. It was speculated that MSH1 gene mediating leaf senescence maybe dependent on the MSH1-regulating the development of chloroplast.