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Genes containing nucleotide-binding sites (NBS) play an important role in pathogen resistance in plants. However, the evolutionary fate of NBS-encoding genes after formation of allotetraploid Brassica napus (AnAnCnCn, 2n = 38) is still unknown. We performed a genome-wide comparison of putatively functional NBS-encoding genes in B. napus and its progenitor species Brassica rapa (ArAr, 2n = 20) and Brassica oleracea (CoCo, 2n = 18), identifying 464, 202, and 146 putatively functional NBS-encoding genes respectively, with genes unevenly distributed in several clusters. The An-subgenome of B. napus possessed similar numbers of NBS-encoding genes (191 genes) to the Ar genome of B. rapa (202 genes) and similar clustering patterns. However, the Cn genome of B. napus had many more genes (273) than the B. oleracea Co genome (146), with different clustering trends. Only 97 NBS-encoding genes (66.4%) in B. oleracea were homologous with NBS-encoding genes in B. napus, while 176 NBS-encoding genes (87.1%) were homologous between B. rapa and B. napus. These results suggest a greater diversification of NBS-encoding genes in the C genome may have occurred after formation of B. napus. Although most NBS-encoding genes in B. napus appeared to derive from the progenitors, the birth and death of several NBS-encoding genes was also putatively mediated by non-homologous recombination. The Ka/Ks values of most homologous pairs between B. napus and the progenitor species were less than 1, suggesting purifying selection during B. napus evolution. The majority of NBS-encoding genes (60% in all species) showed higher expression levels in root tissue (out of root, leaf, stem, seed and flower tissue types). Comparative analysis of NBS-encoding genes with mapped resistance QTL against three major diseases of B. napus (blackleg, clubroot and Sclerotinia stem rot) found 204 NBS-encoding genes in B. napus located within 71 resistance QTL intervals. The majority of NBS-encoding genes were co-located with resistance QTLs against a single disease, while 47 genes were co-located with QTLs against two diseases and 3 genes were co-located with QTLs against all three. Our results revealed significant variation as well as interesting evolutionary trajectories of NBS-encoding genes in the different Brassica subgenomes, while co-localization of NBS-encoding genes and resistance QTL may facilitate resistance breeding in oilseed rape.

In Brassica napus, floral development is a decisive factor in silique formation, and it is influenced by many cultivation practices including planting date. However, the effect of planting date on floral initiation in canola is poorly understood at present. A field experiment was conducted using a split plot design, in which three planting dates (early, 15 September, middle, 1 October, and late, 15 October) served as main plot and five varieties differing in maturity (1358, J22, Zhongshuang 11, Zheshuang 8, and Zheyou 50) employed as subplot. The purpose of this study was to shed light on the process of floral meristem (FM) differentiation, the influence of planting date on growth period (GP) and floral initiation, and silique formation. The main stages of FM developments can be divided into four stages: first, the transition from shoot apical meristem to FM; second, flower initiation; third, gynoecium and androecium differentiation; and fourth, bud formation. Our results showed that all genotypes had increased GPs from sowing to FM differentiation as planting date was delayed while the GPs from FM differentiation to budding varied year by year except the very early variety, 1358. Based on the number of flowers present at the different reproductive stages, the flowers produced from FM differentiation to budding closely approximated the final silique even though the FM differentiated continuously after budding and peaked generally at the middle flowering stage. The ratio of siliques to maximum flower number ranged from 48 to 80%. These results suggest that (1) the period from FM differentiation to budding is vital for effective flower and silique formation although there was no significant correlation between the length of the period and effective flowers and siliques, and (2) the increased number of flowers from budding were generally ineffective. Therefore, maximizing flower numbers prior to budding will improve silique numbers, and reducing FM degeneration should also increase final silique formation. From the results of our study, we offer guidelines for planting canola varieties that differ in maturity in order to maximize effective flower numbers.

High temperature stress is an important abiotic stress during plant growth and development that can damage canola male reproductive organ development. In this present study, we characterized a canola genic male sterile line that its fertility can be restored after high temperature induction with heterozygous but not homozygous condition. Anther length and weight was elongated and increased 2 and 5.7 times at 9 days after high temperature treatment in heterozygous line. Furthermore, viable pollen grain was produced in the anther. Anther carbohydrate content was assayed. The result showed that fructose and sucrose contents were much more stable under heat stress both in hetero- or homozygous lines. However, glucose and starch content was considerably increased after high temperature treatment in heterozygous line. In particular, anther glucose content was twice as much as that of starch content after 5 days high temperature treatment. Activity of neutral invertase, acid invertase, and sucrose synthase were increased in the anther of heterozygous line under heat stress. But activity of neutral invertase was the highest among these three sucrose cleavage enzymes. Both activity of sucrose phosphate synthase and starch phosphorylase were decreased under heat stress in the anther of heterozygous line. Activity of ADP glucose pyrophosphorylase was greatly increased in the heterozygous line, which was beneficial for starch accumulation. Transcription level of carbohydrate related genes was analyzed. 27 and 34 of the carbohydrate related genes were identified for down- and up-regulated in the anther of heterozygous line, respectively. Their function involved in the regulation of heat tolerance of heterozygous line was also discussed. Key words: Canola, carbohydrate, gene.