Abstract
Several mitochondrial-targeted pentatricopeptide repeat (PPR) proteins involved in pollen development have been reported to be fertility restorer (Rf) proteins. However, the roles of plastid-localized PPR proteins in plant male reproduction are poorly defined. Here, we described a plastid-localized PPR-SMR protein, OsPPR676, which is required for plant growth and pollen development in rice. In this study, OsPPR676 was confirmed to be an interacted protein with Osj10gBTF3, β-subunit of nascent polypeptide-associated complex (β-NAC), by bimolecular fluorescence complementation assays, indicating that both proteins are probably involved in the same regulatory pathway of pollen development. Compared with other chloroplast-rich tissues, OsPPR676 was only weakly expressed in anther, but in the Mei and YM stages of pollen development, its expression was relatively strong in the tapetum. Disruption of OsPPR676 resulted in growth retardation of plants and partial sterility of pollens. Phenotypic analysis of different osppr676 mutant lines implied that the SMR domain was not essential for the function of OsPPR676. We further demonstrated that OsPPR676 is essential for production of plastid atpB subunit, and then plays crucial roles in biosynthesis of fatty acids, carbohydrates, and other organic matters via affecting activity of ATP synthase.
Highlights
Rice male sterility is frequently caused by environmental effects or genetic mutation, leading to defective anther development and pollen fertility
To study the function of OsPPR676,we analyzed OsPPR676 sequence, indicating that the OsPPR676 is the orthologue of maize ATP4 and Arabidopsis SVR7
The OsPPR676-green fluorescent protein (GFP) construct and the mitochondrial marker F1-ATPase- γ: RFP were transiently co-expressed in rice protoplasts, which showed that the GFP signal of OsPPR676-GFP was not localized to the mitochondria (Fig. 1d)
Summary
Rice male sterility is frequently caused by environmental effects or genetic mutation, leading to defective anther development and pollen fertility. A specific set of nuclear genes called restorer-of-fertility (Rf) genes, which primarily belong to the pentatricopeptide repeat (PPR) family, are required for the development of a functional male gametophyte in plants with S (sterile) type cytoplasm. RF1A and RF1B are both targeted to mitochondria and can restore rice male fertility by blocking ORF79 production via endonucleolytic cleavage (RF1A) or degradation (RF1B) of dicistronic B-atp6/orf[79] mRNA5. Another PPR protein RF5 interacts directly with a Gly-rich protein GRP162 to form a subunit of restorer fertility complex (RFC), binding to CMS-associated transcripts atp6/orfH79. We first report a plastid-localized PPR-SMR protein OsPPR676 required for both pollen development and plant growth in rice. This work characterized a rice PPR-SMR protein for the first time, and unravelled a probable new mechanism of male sterility in plants
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