Homoploid F1 hybrids and segmental allotetraploids of japonica and indica rice subspecies show similar and enhanced tolerance to nitrogen deficiency than parental lines.

It remains unclear whether the merger of two divergent genomes by hybridization at the homoploid level or coupled with whole-genome duplication (WGD; allopolyploidy) can result in plants having better tolerance to stress conditions. In this study, we compared phenotypic performance and gene expression in the two diploid subspecies of rice (Oryza sativa subsp. japonica and indica), their reciprocal F1 hybrids, and in segmental allotetraploids under normal and nitrogen (N)-deficient conditions. We found that F1 hybrids and tetraploids showed higher and similar levels of tolerance to N deficiency than either parent. In parallel, total expression levels of 18 relevant functional genes were less perturbed by N deficiency in the F1 hybrids and tetraploids than in the parents. This was consistent with stable intrinsic partitioning of allelic/homoeologous expression defined by parental legacy in the homoploid F1 hybrids/tetraploids between the two conditions. The results suggest that genetic additivity at both the homoploid and allopolyploidy level might lead to similar beneficial phenotypic responses to nitrogen stress compared with the parents. The lack of synergistic responses to N limitation concomitant with WGD, relative to that exhibited by F1 hybrids, adds new empirical evidence in support of the emerging hypothesis that hybridization by itself can play a significant role in plant adaptive evolution in times of stress.

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