Bulked Segregant RNA-Seq Analysis of Pollinated Pistils Reveals Genes Influencing Spikelet Fertility in Rice

Prezygotic isolation is important for successful fertilization in rice, significantly affecting yield. This study focused on F_(5:6) generation plants derived from inter-subspecific crosses(Nipponbare × KDML105) with low(LS) and high seed-setting rates(HS), in which normal pollen fertility was observed. However, LS plants showed a reduced number of pollen grains adhering to the stigma and fewer pollen tubes reaching the ovules at 4-5 h post-pollination, compared with HS plants. Bulked segregant RNA-Seq analysis of pollinated pistils from the HS and LS groups revealed 249 and 473 differentially expressed genes(DEGs), respectively. Kyoto Encyclopedia of Genes and Genomes analysis of the HS and LS-specific DEGs indicated enrichment in metabolic pathways, pentose and glucuronate interconversions, and flavonoid biosynthesis. Several of these DEGs exhibited co-expression with pollen development genes and formed extensive clusters of co-expression networks. Compared with LS pistils, enzyme genes controlling pectin degradation, such as OsPME35 and OsPLL9, showed similar expression patterns, with higher levels in HS pistils pre-pollination. Os02g0467600, similar to cinnamate 4-hydroxylase gene(CYP73), involved in flavonoid biosynthesis, displayed higher expression in HS pistils post-pollination. Our findings suggest that OsPME35, OsPLL9, and Os02g0467600 contribute to prezygotic isolation by potentially modifying the stigma cell wall(OsPME35 and OsPLL9) and controlling later processes such as pollen-stigma adhesion(Os02g0467600) genes. Furthermore, several DEGs specific to HS and LS were co-localized with QTLs and functional genes associated with spikelet fertility. These findings provide valuable insights for further research on rice spikelet fertility, ultimately contributing to the development of high-yielding rice varieties.

Experimental hybridization and reproductive isolation between two sympatric species of tephritid fruit flies in the Anastrepha fraterculus species group

Among tephritid fruit flies,hybridization has been found to produce local adaptation and speciation,and in the case of pest species,induce behavioral and ecological alterations that can adversely impact efficient pest management.Thefraterculus species group within Anastrepha (Diptera:Tephritidae),is a rapidly radiating aggregate,which includes cryptic species complexes,numerous sister species,and several pest species. Molecular studies have highlighted the possibility of introgression between A.fraterculus and A.obliqua.Reproductive isolation has been studied among morphotypes of the A. fraterculus species complex as a tool for species delimitation.Here we examined the exis- tence and strength of prezygotic and postzygotic isolation between sympatric populations of two closely related species within the highly derivedfraterculus group (A.fraterculus and A.obliqua),coexisting in nature.Although adults of both species showed a strong tendency for assortative mating,a small proportion of hybrid pairings in both directions were observed.We also observed asymmetric postzygotic isolation,with one hybrid cross displaying a strong reduction in fecundity and F1 egg fertility.Survival was greater for the progeny of homotypic and hybrid crosses in the maternal host.There was a marked female biased sex ratio distortion for both F1 hybrid adults.Hybridization between A.fraterculus and A.obliqua in nature may be difficult but possible;these two species display stronger reproductive isolation than all pairs of species previously examined in the A.fraterculus species complex.Asymmetric postzygotie isolation is suggestive of Wolbachia mediated cytoplasmic incompatibilities that may be exploited in area-wide pest management.