Maize PPR278 Functions in Mitochondrial RNA Splicing and Editing.

Jing Yang,Xinhai Li,Yang Cui,Zhijia Yang,Jingang Liang,Xiangbo Zhang,Jinsheng Lai,Weibin Song

doi:10.3390/ijms23063035

Abstract

Pentatricopeptide repeat (PPR) proteins are a large protein family in higher plants and play important roles during seed development. Most reported PPR proteins function in mitochondria. However, some PPR proteins localize to more than one organelle; functional characterization of these proteins remains limited in maize (Zea mays L.). Here, we cloned and analyzed the function of a P-subfamily PPR protein, PPR278. Loss-function of PPR278 led to a lower germination rate and other defects at the seedling stage, as well as smaller kernels compared to the wild type. PPR278 was expressed in all investigated tissues. Furthermore, we determined that PPR278 is involved in the splicing of two mitochondrial transcripts (nad2 intron 4 and nad5 introns 1 and 4), as well as RNA editing of C-to-U sites in 10 mitochondrial transcripts. PPR278 localized to the nucleus, implying that it may function as a transcriptional regulator during seed development. Our data indicate that PPR278 is involved in maize seed development via intron splicing and RNA editing in mitochondria and has potential regulatory roles in the nucleus.

Highlights

Pentatricopeptide repeat (PPR) proteins are widely distributed in plants, with more than 400 members in maize (Zea mays L.) [1], which were divided into two subfamilies: The P subfamily containing motif P only, and the PLS subfamily harboring the P, L, and S motifs [2,3]
Our findings demonstrate that PPR278 affects seed development via effects on RNA intron splicing and editing in mitochondria and on gene expression in nuclei, expanding our limited knowledge about the function of P-subfamily PPR proteins that are capable of splicing introns
We isolated a kernel mutant from our mutant libraries established by an ethyl methanesulfonate (EMS)-based method, which produced smaller seeds compared to the wild type (WT) (Figure 1A–D), and named it ppr278-1 based on similar phenotypes with other ppr mutants in maize

Summary

Introduction

Pentatricopeptide repeat (PPR) proteins are widely distributed in plants, with more than 400 members in maize (Zea mays L.) [1], which were divided into two subfamilies: The P subfamily containing motif P only, and the PLS subfamily harboring the P, L, and S motifs [2,3]. Ongoing work has shown that PPR proteins splice 22 group II introns present within 8 protein-coding genes in mitochondria in maize, including NADH dehydrogenase subunits , and 7 (nad1, 2, 4, 5, 7), and subunits of a complex involved in the biogenesis of cytochrome c: subunits F (ccmFC), cytochrome c oxidase subunits (cox2), and ribosomal protein s3 (rps3) [6–8]. Loss-function of PPR proteins and/or other spliceosomes results in defects in seed and/or seedling development, such as an empty pericarp in the seed, decreased 100-kernel weight, and seedling death, due to abnormal intron splicing of mitochondrial genes, which leads to abnormal assembly of mitochondrial complex I and insufficient production of energy molecules [9–26] These findings highlight the importance of PPR-based RNA splicing in mitochondria for seed development in maize

Methods

Results

Conclusion