Study of the C genome QTL affecting flowering time in spring oilseed Brassica napus under a short-day condition

Abstract

Brassica napus, mostly known as canola, is an important oilseed crop in Canada. Earliness of flowering and maturity are one of the important traits for growing spring canola in North America. These traits can be improved through identification of the genes and alleles affecting flowering time and understanding their effect on other traits. In this study, near-isogenic lines (NILs) carrying flowering time QTL alleles of Brassica oleracea or B. napus which located on C1 or C9 chromosome were evaluated under 10 hr photoperiod condition for morphological and root and shoot biomass traits to understand the effect of these QTL alleles on the other traits. The NILs carrying C1 or C9 allele of B. oleracea flowered earlier, as expected, and no visible difference was observed between the NILs and the recurrent parent for leaf characteristics. However, the NILs showed significant difference for plant height, shoot and root biomass indicating that the flowering time QTL alleles may exert pleiotropic effect on these traits or QTL affecting these traits are located in the same genomic region. This thesis research also included expression analysis of putative flowering time genes from C5 and C9 flowering time QTL. For this, a set of early- and late-flowering B. napus lines developed from a B. napus × B. oleracea interspecific cross were used, and expression analysis of 30 flowering genes from C5 (15) and C9 (15) QTL was carried out on leaf and shoot apex tissue collected from the plants grown under 10 hr photoperiod condition. A majority of the genes showed a greater expression at night than in morning, and significant differential expression was observed for CO, PHYA, FT, AP2, SOC1 and TEM1; this suggests that these genes might be involved in flowering time variation between the early and late flowering lines. The leaf materials of the above-mentioned early- and late-flowering plants were also used in a proteomic study to identify the proteins involved in flowering time variation. This study identified the proteins involved in photosynthesis, pigmentation, phytohormone signaling, stress response, ROS, ion binding, mRNA binding, protein binding and many others. Thus, this thesis research showed that the flowering time alleles can exert effect on other morphological and physiological traits, and the research also identified the genes and proteins potentially involved in the regulation of flowering time in canola under short-day photoperiod conditions.