Organelle genome composition and candidate gene identification for Nsa cytoplasmic male sterility in Brassica napus.

BACKGROUND: Nsa cytoplasmic male sterility (CMS) is a novel alloplasmic male sterility system derived from somatic hybridization between Brassica napus and Sinapis arvensis. Identification of the CMS-associated gene is a prerequisite for a better understanding of the origin and molecular mechanism of this CMS. With the development of genome sequencing technology, organelle genomes of Nsa CMS line and its maintainer line were sequenced by pyro-sequencing technology, and comparative analysis of the organelle genomes was carried out to characterize the organelle genome composition of Nsa CMS as well as to identify the candidate Nsa CMS-associated genes. RESULTS: Nsa CMS mitochondrial genome showed a higher collinearity with that of S. arvensis than B. napus, indicating that Nsa CMS mitochondrial genome was mainly derived from S. arvensis. However, mitochondrial genome recombination of parental lines was clearly detected. In contrast, the chloroplast genome of Nsa CMS was highly collinear with its B. napus parent, without any evidence of recombination of the two parental chloroplast genomes or integration from S. arvensis. There were 16 open reading frames (ORFs) specifically existed in Nsa CMS mitochondrial genome, which could not be identified in the maintainer line. Among them, three ORFs (orf224, orf309, orf346) possessing chimeric and transmembrane structure are most likely to be the candidate CMS genes. Sequences of all three candidate CMS genes in Nsa CMS line were found to be 100% identical with those from S. arvensis mitochondrial genome. Phylogenetic and homologous analysis showed that all the mitochondrial genes were highly conserved during evolution. CONCLUSIONS: Nsa CMS contains a recombined mitochondrial genome of its two parental species with the majority form S. arvensis. Three candidate Nsa CMS genes were identified and proven to be derived from S. arvensis other than recombination of its two parental species. Further functional study of the candidate genes will help to identify the gene responsible for the CMS and the underlying molecular mechanism.

[The discovery and genetic analysis of dwarf mutation 99CDAM in Brassica napus L].

The plant height of rapeseed varieties has increased more than 20 cm due to wide application of heterosis, which leads to high risk of lodging at late stages of rapeseed development. Using dwarf genes to decrease plant height is an effective approach to resolve the lodging problem. A dwarf mutation 99CDAM with plant height of about 85 cm was discovered from a Brassica napus line which had selfed for many years. The mutation 99CDAM has good characters of early flowering and rich branches, as well as better yield and quality traits, which can be stably inherited, so 99CDAM has important value in Brassica napus breeding. Genetic analysis on reciprocal crosses between 99CDAM with high-stalk lines 2091, 7045 and 7350, and the F2BC1 and F2:3 populations derived from the cross between 2091 with 99CDAM indicated that the genetic model of dwarf genes in 99CDAM was obviously different from what had been reported before. The mutation 99CDAM was controlled by three pairs of recessive dwarf genes and showed a maternal effect..