Abstract
Double pollen fertility neutral genes, San and Sbn, can control pollen sterility in intersubspecific (indica × japonica) rice hybrids, which has excellent potential to increase rice yield. Previous studies showed that polyploidy could increase the interaction of three pollen sterility loci, i.e. Sa, Sb and Sc, which cause pollen sterility in autotetraploid rice hybrids, and hybrid fertility could be improved by double neutral genes, San and Sbn, in autotetraploid rice hybrids. We compared cytological and transcriptome data between autotetraploid and diploid rice hybrid during meiosis and single microspore stages to understand the molecular mechanism of neutral genes for overcoming pollen sterility in autotetraploid rice hybrids, which harbored double neutral genes. Cytological results revealed that the double neutral genes resulted in higher pollen fertility (76.74%) and lower chromosomal abnormalities in autotetraploid hybrid than in parents during metaphase I, metaphase II, anaphase I and anaphase II. Moreover, autotetraploid rice hybrid displayed stronger heterosis than a diploid hybrid. Compared with diploid rice hybrid, a total of 904 and 68 differently expressed genes (DEGs) were identified explicitly in autotetraploid hybrid at meiosis and single microspore stages, respectively. Of these, 133 and 41 genes were detected in higher-parent dominance and transgressive up-regulation dominance, respectively, which were considered autotetraploid potential heterosis genes, including a meiosis-related gene (Os01g0917500, MSP1) and two meiosis specific-genes (Os07g0624900 and Os04g0208600). Gene Ontology (GO) and Kyoto Encyclopedia of Gene and Genomes pathway (KEGG) analysis revealed that DEGs significantly enriched in amino acid metabolism and photosynthesis metabolism. These results indicated that meiosis-specific and meiosis-related genes, and amino acids and photosynthesis metabolism-related genes contribute to higher yield and pollen fertility in autotetraploid rice hybrid. This study provides a theoretical basis for molecular mechanisms of heterosis in autotetraploid rice harboring double neutral genes for pollen fertility.
Highlights
Rice is one of the most key cereal crops which feeds more than half of the world’s population and is essential to food security
Pollen fertility was 68.67%, which was lower than its parents, and mid parent heterosis (MPH) and high parent heterosis (HPH) values for pollen fertility were -24.17% and -24.98%, respectively
We detected high pollen fertility (>65%) in different ploidy hybrids with double neutral genes at Sa and Sb pollen sterility loci, and these results showed that different ploidy hybrids had no interaction at Sa and Sb loci
Summary
Rice is one of the most key cereal crops which feeds more than half of the world’s population and is essential to food security. Indica-japonica hybrid rice has shown more substantial yield potential. Partial sterility has been a significant barrier to the utilization of the strong heterosis present in intersubspecific hybrids. Pollen fertility of indica-japonica hybrids is controlled by at least six loci (Sa, Sb, Sc, Sd, Se and Sf), which showed that it is a complex phenomenon. Neutral alleles for pollen fertility (Sn) that do not interact with typical indica (Si) and japonica (Sj) alleles provide a platform to exploit the strong hybrid vigor derived from intersubspecific crosses by controlling the reproductive obstacles between japonica and indica hybrids. Substantial evidence has shown that neutral genes, San, Sbn, Scn, Sdn, and Sen, provide valuable gene resources to surmount the pollen sterility related to the respective locus [4,5,6,7,8]
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