*Article* **Di**ff**erential RNA Editing and Intron Splicing in Soybean Mitochondria during Nodulation**

**Yuzhe Sun 1, Min Xie 2,3, Zhou Xu 1, Koon Chuen Chan 1, Jia Yi Zhong 1, Kejing Fan 2,3, Johanna Wong-Bajracharya 2,3, Hon-Ming Lam 2,3,\* and Boon Leong Lim 1,2,\***


Received: 8 November 2020; Accepted: 7 December 2020; Published: 9 December 2020

**Abstract:** Nitrogen fixation in soybean consumes a tremendous amount of energy, leading to substantial differences in energy metabolism and mitochondrial activities between nodules and uninoculated roots. While C-to-U RNA editing and intron splicing of mitochondrial transcripts are common in plant species, their roles in relation to nodule functions are still elusive. In this study, we performed RNA-seq to compare transcript profiles and RNA editing of mitochondrial genes in soybean nodules and roots. A total of 631 RNA editing sites were identified on mitochondrial transcripts, with 12% or 74 sites differentially edited among the transcripts isolated from nodules, stripped roots, and uninoculated roots. Eight out of these 74 differentially edited sites are located on the *matR* transcript, of which the degrees of RNA editing were the highest in the nodule sample. The degree of mitochondrial intron splicing was also examined. The splicing efficiencies of several introns in nodules and stripped roots were higher than in uninoculated roots. These include *nad1* introns 2/3/4, *nad4* intron 3, *nad5* introns 2/3, *cox2* intron 1, and *ccmFc* intron 1. A greater splicing efficiency of *nad4* intron 1, a higher NAD4 protein abundance, and a reduction in supercomplex I + III2 were also observed in nodules, although the causal relationship between these observations requires further investigation.

**Keywords:** complex I; intron splicing; maturase; NDH; RNA editing; mitochondria
