Center for Gene Research, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan.
Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya, 464-8601, Japan.
Plant Mol Biol. 2021 Nov;107(4-5):417-429. doi: 10.1007/s11103-020-01090-z. Epub 2020 Oct 31.
Moss PPR-SMR protein PpPPR_64 is a pTAC2 homolog but is functionally distinct from pTAC2. PpPPR_64 is required for psaA gene expression and its function may have evolved in mosses. The pentatricopeptide repeat (PPR) proteins are key regulatory factors responsible for the control of plant organellar gene expression. A small subset of PPR proteins possess a C-terminal small MutS-related (SMR) domain and have diverse roles in plant organellar biogenesis. However, the function of PPR-SMR proteins is not fully understood. Here, we report the function of PPR-SMR protein PpPPR_64 in the moss Physcomitrium patens. Phylogenetic analysis indicated that PpPPR_64 belongs to the same clade as the Arabidopsis PPR-SMR protein pTAC2. PpPPR_64 knockout (KO) mutants grew autotrophically but with reduced protonemata growth and the poor formation of photosystems' antenna complexes. Quantitative reverse transcription-polymerase chain reaction and RNA gel blot hybridization analyses revealed a significant reduction in transcript levels of the psaA-psaB-rps14 gene cluster but no alteration to transcript levels of most photosynthesis- and non-photosynthesis-related genes. In addition, RNA processing of 23S-4.5S rRNA precursor was impaired in the PpPPR_64 KO mutants. This suggests that PpPPR_64 is specifically involved in the expression level of the psaA-psaB-rps14 gene and in processing of the 23S-4.5S rRNA precursor. Our results indicate that PpPPR_64 is functionally distinct from pTAC2 and is a novel PPR-SMR protein required for proper chloroplast biogenesis in P. patens.
莫斯 PPR-SMR 蛋白 PpPPR_64 是 pTAC2 的同源物，但在功能上与 pTAC2 不同。PpPPR_64 是 psaA 基因表达所必需的，其功能可能在苔藓植物中进化而来。五肽重复（PPR）蛋白是负责植物细胞器基因表达调控的关键调节因子。一小部分 PPR 蛋白具有 C 端小 MutS 相关（SMR）结构域，在植物细胞器生物发生中具有多种功能。然而，PPR-SMR 蛋白的功能尚未完全了解。在这里，我们报告了 PPR-SMR 蛋白 PpPPR_64 在苔藓植物Physcomitrium patens 中的功能。系统发育分析表明，PpPPR_64 属于与拟南芥 PPR-SMR 蛋白 pTAC2 相同的进化枝。PpPPR_64 敲除（KO）突变体能够自养生长，但原丝体生长和光系统天线复合物的形成较差。定量逆转录聚合酶链反应和 RNA 凝胶印迹杂交分析显示，psaA-psaB-rps14 基因簇的转录本水平显著降低，但大多数光合作用和非光合作用相关基因的转录本水平没有改变。此外，PpPPR_64 KO 突变体中 23S-4.5S rRNA 前体的 RNA 加工受到损害。这表明 PpPPR_64 特异性参与 psaA-psaB-rps14 基因的表达水平以及 23S-4.5S rRNA 前体的加工。我们的结果表明，PpPPR_64 在功能上不同于 pTAC2，是 P. patens 中正确叶绿体生物发生所必需的新型 PPR-SMR 蛋白。
