BnaC9.SMG7b functions as a positive regulator of number of seeds per silique in rapeseed (Brassica napus L.) by regulating the formation of functional female gametophytes

Abstract

Number of seeds per silique (NSS) is an important determinant of seed yield potential in Brassicaceae crops, and it is controlled by naturally occurring quantitative trait loci. We previously mapped a major quantitative trait locus, qSS.C9, on the C9 chromosome that controls NSS in Brassica napus. To gain a better understanding of how qSS.C9 controls NSS in B. napus, we isolated this locus through a map-based cloning strategy. qSS.C9 encodes a predicted small protein with 119 amino acids, designated as BnaC9.SMG7b, that shows homology with the Ever ShorterTelomere1 tertratricopeptide repeats and Ever Shorter Telomere central domains of Arabidopsis (Arabidopsis thaliana) SUPPRESSOR WITH MORPHOGENETIC EFFECTS ON GENITALIA7 (SMG7). BnaC9.SMG7b plays a role in regulating the formation of functional female gametophyte, thus determining the formation of functional megaspores and then mature ovules. Natural loss or artificial knockdown of BnaC9. SMG7b significantly reduces the number of functional ovules per silique and thus, results in decreased seed number, indicating that qSS.C9 is a positive regulator of NSS in B. napus. Sequence and function analyses show that BnaC9.SMG7b experiences a subfunctionalization process that causes loss of function in nonsense-mediated mRNA decay, such as in Arabidopsis SMG7. Haplotype analysis in 84 accessions showed that the favorable BnaC9.SMG7b alleles are prevalent in modern B. napus germplasms, suggesting that this locus has been a major selection target of B. napus improvement. Our results represent the first step toward unraveling the molecular mechanism that controls the natural variation of NSS in B. napus.Elite Brassica spp. (majorly Brassica napus) with low erucic and glucosinolate content is the third leading source of both vegetable oil and oil extraction meal worldwide (Rondanini et al., 2012). Yield enhancement has been one of the most important goals of B. napus production and genetic improvement. As a complex quantitative trait, the seed yield of a B. napus plant is comprehensively determined by three components: number of seeds per silique (NSS), number of siliques per plant, and seed weight, all of which are typical quantitative traits (Clarke and Simpson, 1978). Although there is rich variation for each of the three components (Zhang et al., 2012a), it is critical to balance the three traits during the breeding program, because significant negative correlations among them have been extensively observed Zhang et al., 2011). Thus, it is highly desirable to identify the genes responsible for each component and subsequently, understand the genetic mechanisms underlying the natural variations. Toward this goal, a large number of quantitative trait loci (QTLs) associated with these yield components in B. napus has been identified in different mapping populations (Quijada et al.,

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

“…It should be noted that the numbers of ovules per ovary were significantly larger than the corresponding numbers of seeds per pod for all of the nine lines ( Figures 1B, 6 ), in accordance with the previous studies (Li et al, 2014; Li, 2015). This suggested that the number of ovules/seeds per ovary/pod should decrease from flowering to maturity.…”

“…It should be noted that the number of seeds per pod for the elite cultivar Zhongshuang11 is much more less than the number of ovules per ovary as well as its maximum reported in the current ( Figure 6 ) and previous (Li et al, 2014; Li, 2015) studies. In addition, both the fertilization rate of ovules and the survival rate of fertilized ovules for the elite cultivar Zhongshuang11 were less than the maximum observed in the current studies ( Figure 8 ).…”

“…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. et al, 2015).…”

Genetic and signalling pathways of dry fruit size: targets for genome editing‐based crop improvement

“…The overexpression of BcRISP1 in Arabidopsis showed reduced seed set and short siliques, which is caused by the reduced pollen formation and impaired pollen tube elongation due to the interruption of the mitochondrial electron transport chain by affecting the expression of mitochondrial breathing chain‐related genes (Liu et al , ). A major QTL qSS.C9 for seeds per silique has been cloned on the C9 chromosome of Brassica napus (Li et al , ), which encodes a predicted small protein with 119 amino acids homologous to the Arabidopsis SMG7 gene that is involved in meiotic cell cycle. The BnaC9.SMG7b was mainly expressed in the vascular tissue of various organs, including cotyledons, rosette leaves, roots, young pedicels and pistils, but not in stamens, petals, stems and mature siliques.…”

MS5 Mediates Early Meiotic Progression and Its Natural Variants May Have Applications for Hybrid Production in Brassica napus

“…The stained samples were mounted in 30% glycerol and observed under an Axio Scope A1 fluorescence microscope (Carl Zeiss) with a UV filter. Observation for callose deposition in the meiotic megasporocytes and megaspores was as described (Li et al, 2015).…”