OsPPR939, a nad5 splicing factor, is essential for plant growth and pollen development in rice

Abstract

Key message P-subfamily PPR protein OsPPR939, which can be phosphorylated by OsS6K1, regulates plant growth and pollen development by involving in the splicing of mitochondrial nad5 introns 1, 2, and 3. Abstract In land plants, pentatricopeptide repeat (PPR) proteins play key roles in mitochondrial group II intron splicing, but how these nucleus-encoded proteins are imported into mitochondria is unknown. To date, a few PPR proteins have been characterized in rice (Oryza sativa). Here, we demonstrate that the mitochondrion-localized P-subfamily PPR protein OsPPR939 is required for the splicing of nad5 introns 1, 2, and 3 in rice. Complete knockout or partial disruption of OsPPR939 function resulted in different degrees of growth retardation and pollen sterility. The dramatically reduced splicing efficiency of these introns in osppr939-4 and osppr939-5 led to reduced mitochondrial complex I abundance and activity and enhanced expression of alternative respiratory pathway genes. Complementation with OsPPR939 rescued the defective plant morphology of osppr939-4 and restored its decreased splicing efficiency of nad5 introns 1, 2, and 3. Therefore, OsPPR939 plays crucial roles in plant growth and pollen development by splicing mitochondrial nad5 introns 1, 2, and 3. More importantly, the 12th amino acid Ser in the N-terminal targeting sequence of OsPPR939 is phosphorylated by OsS6K1, and truncated OsPPR939 with a non-phosphorylatable S12A mutation in its presequence could not be imported into mitochondria, suggesting that phosphorylation of this amino acid plays an important role in the mitochondrial import of OsPPR939. To our knowledge, the 12th residue Ser on OsPPR939 is the first experimentally proven phosphorylation site in PPR proteins. Our results provide a basis for investigating the regulatory mechanism of PPR proteins at the post-translational level.

Alternative splicing during fruit development among fleshy fruits

“…In maize ( Zea mays L.), researchers have found that missplicing of U12-type introns in rgh3 can cause aberrant endosperm cell differentiation and proliferation [ 16 ]. In rice ( Oryza sativa ), OsPPR939 plays crucial roles in plant growth and pollen development by splicing introns 1, 2, and 3 of mitochondrial nad5 [ 17 ]. Fruits can be divided into fleshy fruits and dry fruits according to the types of fruit walls [ 18 ].…”

Rice FLOURY SHRUNKEN ENDOSPERM 5 Encodes a Putative Plant Organelle RNA Recognition Protein that Is Required for cis-Splicing of Mitochondrial nad4 Intron 1

“…Without support from heterozygous maternal tissues, the response in homozygous seedlings or calli is perhaps weakened or abolished. Thus, small subcomplexes were not observed in the fse5 mutant or rice ppr mutants such as fgr1, flo10 and osppr939 (Hao et al 2019;Wu et al 2019;Zheng et al 2021).…”

“…OsActin1 was used as an internal control for data normalization. The values are the means ± SDs Homozygous immature dek35 kernels were used to extract crude mitochondria for BN-PAGE, whereas homozygous seedlings or calli (−/−) are usually used in the case of rice (Hao et al 2019;Wu et al 2019;Zheng et al 2021). In this study, homozygous fse5 seedlings were used for BN-PAGE.…”

A mitochondrial pentatricopeptide repeat protein enhances cold tolerance by modulating mitochondrial superoxide in rice

“…Mutants of these PPR genes lead to complete abolishment of intact complex I and result in severe seed developmental defects, highlighting the importance of complex I for seed development. By contrast, only a few proteins in rice were identified to function in mitochondrial intron splicing, such as OsPPR939 for nad5 intron 1, 2, 3 40 and RL1 for nad4 intron 1 41 . Here, we identified SOP10 and showed it participates in splicing of nad4 and nad5 intron1 and RNA editing of nad2 and nad6 .…”