Abstract
Glutaredoxins (Grxs) are a ubiquitous group of oxidoreductase enzymes that are important in plant growth and development; however, the functions of rice Grxs have not been fully elucidated. In this paper, we showed that one of the Grxs, encoded by OsGrxC2.2, exhibited Grx activity. Furthermore, we demonstrated that OsGrxC2.2 was able to regulate embryo development during embryogenesis. Transgenic rice lines overexpressing OsGrxC2.2 unexpectedly exhibited degenerate embryos as well as embryoless seeds. Our data indicated that the embryonic abnormalities occurred at an early stage during embryogenesis. We found that the expression of several endodermal layer marker genes for embryo development, such as OSH1 (apical region marker), OsSCR (L2 ground tissue marker), and OsPNH1 (L3 vascular tissue marker), were significantly decreased in the OsGrxC2.2-overexpressed transgenic rice lines. In contrast, the transcript levels of the majority of protodermal layer markers, including HAZ1, ROC2, ROC3, and RAmy1A, and the shoot apical meristem marker HB, showed little change between the wild-type (WT) and OsGrxC2.2-overexpressing embryos. Surprisingly, the seed weight of the overexpressed transgenic rice was remarkably increased in comparison to that of the WT. These results indicate that the overexpression of OsGrxC2.2 interferes with the normal embryogenesis of rice embryos and leads to increased grain weight. To the best of our knowledge, this is the first report that OsGrxC2.2 is a rice embryo development-associated gene.
Highlights
Rice (Oryza sativa L.) is the predominant staple food for more than half of the global human population
In all the examined tissues and organs, OsGrxC2.2 was found to be highly expressed in the leaf, flag leaf, and developing seeds at different stages compared to the root, stem, tiller, and panicle (Figure 1A)
The yellow fluorescent protein (YFP) signal of the OsGrxC2.2-YFP fusion protein was visualized under a confocal microscope, which demonstrated that the OsGrxC2.2 protein was expressed and localized in the cytoplasm (Supplementary Figure S1)
Summary
Rice (Oryza sativa L.) is the predominant staple food for more than half of the global human population. Only accounting for 2–3% of the seed weight, the rice embryo is crucial for plant growth. Advancing our understanding of the molecular mechanisms of rice embryogenesis is important and could be used to improve grain weight and seed quality. Rice mutants with an embryonic lethal phenotype have been identified and characterized, and several genes have been used as molecular markers for rice embryogenesis studies (Hong et al, 1995; Di Laurenzio et al, 1996; Kamiya et al, 2003; Ito et al, 2004). Despite these advancements in phenotypic identification, the molecular mechanisms of rice embryogenesis remain largely unknown
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