Mechanism Of Hybrid Sterility Research Articles

Integrated miRNA and mRNA Sequencing Reveals the Sterility Mechanism in Hybrid Yellow Catfish Resulting from Pelteobagrus fulvidraco (♀) × Pelteobagrus vachelli (♂).

The hybrid yellow catfish exhibits advantages over pure yellow catfish in terms of fast growth, fast development, a high feeding rate, and strong immunity; additionally, it is almost sterile, thus ensuring the conservation of the genetic stock of fish populations. To investigate the sterility mechanism in hybrid yellow catfish (P. fulvidraco (♀) × P. vachelli (♂)), the mRNA and miRNA of the gonads of P. fulvidraco, P. vachelli, and a hybrid yellow catfish were analyzed to characterize the differentially expressed genes; this was carried out to help establish gene expression datasets to assist in the further determination of the mechanisms of genetic sterility in hybrid yellow catfish. In total, 1709 DEGs were identified between the hybrid and two pure yellow catfishes. A KEGG pathway analysis indicated that several genes related to reproductive functions were upregulated, including those involved in the cell cycle, progesterone-mediated oocyte maturation, and oocyte meiosis, and genes associated with ECM-receptor interaction were downregulated. The spermatogenesis-related GO genes CFAP70, RSPH6A, and TSGA10 were identified as being downregulated DEGs in the hybrid yellow catfish. Sixty-three DEmiRNAs were identified between the hybrid and the two pure yellow catfish species. The upregulated DEmiRNAs ipu-miR-194a and ipu-miR-499 were found to target the spermatogenesis-related genes CFAP70 and RSPH6A, respectively, playing a negative regulatory role, which may underscore the miRNA-mRNA regulatory mechanism of sterility in hybrid yellow catfish. The differential expression of ipu-miR-196d, ipu-miR-125b, and ipu-miR-150 and their target genes spidr, cep85, and kcnn4, implicated in reproductive processes, was verified via qRT-PCR, consistent with the transcriptome sequencing expression trends. This study provides deep insights into the mechanism of hybrid sterility in vertebrate groups, thereby contributing to achieving a better understanding and management of fish conservation related to hybrid sterility.

Progress of <italic>indica-japonica</italic> hybrid sterility and wide-compatibility in rice

As a main staple food for world population, utilization of heterosis in rice has increased crop productivity tremendously. The Asian cultivated rice ( Oryza sativa L.) consists of two subspecies, indica and japonica . Genetic differentiation between indica and japonica subspecies appears to be a major source of genetic diversity in the cultivated rice gene pool. A strategic plan for utilization of inter-subspecific heterosis was proposed half a century ago, indicating that strong heterosis in indica-japonica hybrids provides an effective approach to increase the yield potential for rice breeding. Hybrid sterility that caused by postzygotic reproductive isolation has been a major barrier for utilization of such heterosis between indica and japonica . Genetic analyses have identified a large number of loci conditioning hybrid sterility in rice, which regulate fertility in heterozygous genetic background by complex allelic and epistasis interactions. Six locus-pairs regulating hybrid embryo-sac or pollen sterility have been cloned recently in rice, providing fresh understandings in mechanism of hybrid sterility. The molecular and evolutionary mechanisms underlying reproductive isolation are summarized with respect to the rice hybrid sterility genes, which reveal three evolutionary genetic models including the parallel divergence model, the sequential divergence model, and the parallel-sequential divergence model. There also exists a special group of rice germplasm, referred to as wide-compatibility varieties that produce fertile hybrids when crossed to both indica and japonica varieties. The wide-compatibility genes in these varieties enable hybridization and provide valuable genetic resources for utilization of inter-subspecific heterosis, which take diverse forms owing to the divergent mechanisms in reproductive barriers. Therefore, understanding in hybrid sterility and reproductive isolation in rice would greatly facilitate the utilization of heterosis in breeding programs. This paper summarized the progress in genetic and molecular mechanisms regulating rice hybrid sterility, and discussed the recent understanding in wide-compatibility genes and their utilizations in breeding of wide-compatibility varieties. These advances may greatly facilitate the exploration of inter-subspecific heterosis in breeding programs.

Mechanisms of Speciation

Mechanisms of Speciation

Fine mapping of a gene responsible for pollen semi-sterility in hybrids between Oryza sativa L. and O. glaberrima Steud

Asian cultivated rice (Oryza sativa L.) and African cultivated rice (Oryza glaberrima Steud.) are the two main cultivated rice species in the world, with strong heterosis in their F1 hybrids. However, hybrid sterility is a major barrier, although significant heterosis has been observed. In this study, an F1 pollen semi-sterility locus, S19, was identified on rice chromosome 3 by using near-isogenic lines derived from repeated backcross and marker-assisted selection. The typical pollen semi-sterility was observed in F1 hybrids between S19-NIL and Dianjingyou 1. Cytological study of pollen developmental stages indicated that pollen abortion occurred at the late binucleate stage because of a starch accumulation obstacle in some pollen grains. Molecular analysis revealed that the semi-sterility was caused by the abortion of most male gametophytes carrying the S19 allele from the japonica variety Dianjingyou 1. In a population of 12,780 F2 plants derived from S19-NIL/Dianjingyou 1, the S19 locus was fine-mapped to a chromosomal region of 54 kb based on BAC clones of cv. Nipponbare. Interestingly, an addition of a DNA fragment of about 89 kb to the 54-kb region was found in S19-NIL based on BAC clones of O. glaberrima. Gene prediction analysis identified 12 open reading frames (ORF) based on the region of Dianjingyou 1, while 32 ORFs were predicted in S19-NIL. Map-based cloning of this gene will help us to understand the underlying mechanism of hybrid sterility between the two cultivated rice species.