Genetic architecture and mechanism of seed number per pod in rapeseed: elucidated through linkage and near-isogenic line analysis

Abstract

Seed number per pod (SNPP) is one of the major yield components and breeding targets in rapeseed that shows great variation and is invaluable for genetic improvement. To elucidate the genetic architecture and uncover the mechanism of SNPP, we identified five quantitative trait loci (QTLs) using the BnaZNRIL population, which were integrated with those of previous studies by physical map to demonstrate a complex and relatively complete genetic architecture of SNPP. A major QTL, qSN.A6, was successfully fine-mapped from 1910 to 267 kb using near-isogenic line (NIL). In addition, qSN.A6 exhibited an antagonistic pleiotropy on seed weight (SW), which is caused by a physiological interaction in which SNPP acts “upstream” of SW. Because the negative effect of qSN.A6 on SW cannot fully counteract its positive effect on SNPP, it also enhanced the final yield (17.4%), indicating its great potential for utilization in breeding. The following genetic and cytological experiments further confirmed that the different rate of ovule abortion was responsible for the ~5 seed difference between Zhongshuang11 and NIL-qSN.A6. This systematic approach to dissecting the comprehensive genetic architecture of SNPP and characterizing the underlying mechanism has advanced the understanding of SNPP and will facilitate the development of high-yield cultivars.

Genetic and Cytological Analyses of the Natural Variation of Seed Number per Pod in Rapeseed (Brassica napus L.)

“…At each stage, three flowers/pods were sampled from the marked positions of 10 representative plants and used to observe the number of ovules/seeds per ovary/pod. The detailed procedures were performed as our previous study (Yang et al, 2016). …”

“…Then, the ovules were peeled off from the ovaries, dehydrated through an ethanol series of 75, 85, 95, and 100%, and embedded in the paraffin. The detailed experimental procedures for section were as described in the previous studies (Li et al, 2014; Yang et al, 2016). Generally, a total of 30–40 ovules have got the successful sections for each individual.…”

“…To investigate the pollen germination rate in vitro , the pollens were quickly shaken off from the three sampled flowers of each individual to spread evenly on the pollen germination medium, cultured at room temperature for 3 h, and then observed using the fluorescence microscope. The detailed experimental procedures were as described in the previous studies (Sato et al, 1998; Fan et al, 2012; Yang et al, 2016). …”

“…From the applied perspective, seed number is one of the most important factors of yield composition and also one of the major targets for genetic improvement in most crops, including rapeseed (Yang et al, 2016). …”

“…The SNPP in rapeseed is multiply determined by its components t , including the number of ovules per ovary, the proportion of ovules to be fertilized (=the proportion of fertile ovules × the proportion of fertile ovules to be fertilized), and the proportion of fertilized ovules to develop into seeds. In rapeseed, the number of ovules per ovary is determined by the ovule differentiation process (Yang et al, 2016). The proportion of ovules to be fertilized is determined at the fertilization process, which is dependent on many factors such as ovule fertility, pollen sterility, the interaction between the pollen grain/pollen tube including the sperm cells with the various sporophytic maternal tissues, and the cells of the female gametophyte (Dresselhaus and Franklin-Tong, 2013; Li et al, 2014; Li S.P.…”