**5. Conclusions**

In this study, we characterized one *yellow leaf* mutant and identified *YL*, a soybean homolog of *Arabidopsis ORRM1* that is involved in RNA editing. The *yl* mutant displayed yellow leaves, reduced chlorophyll contents, impaired photosynthesis and an altered chloroplast ultrastructure. Through fine mapping, the *yl* mutation was narrowed down to a 28-kb genomic region in chromosome 20 between markers S3 and S7-3. DNA sequencing revealed that the *YL* mutation in the *yl* mutant is a C to A transition in *Glyma.20G187000*, which causes an amino acid alteration. Further function analysis of *YL* uncovered that the point mutation in *yl* influenced the editing extent in 42% of the chloroplast sites surveyed. However, we speculate that only the decreased level of conversion of cytidine to uridine at *petB*-611 and *psbL*-2 may affect normal photosynthesis in *yl* leaves. Together, our findings indicate that soybean YL protein influences photosynthesis, possibly via its function in chloroplast RNA editing.

**Supplementary Materials:** Supplementary materials can be found at http://www.mdpi.com/1422-0067/21/12/4275/ s1. Table S1. Comparison of the extent of RNA editing of chloroplast sites between the wild type and *yl* mutant by RNA-seq. Table S2. Verification of the extent of chloroplast RNA editing by Sanger sequencing. Table S3. Primers used in this study.

**Author Contributions:** B.Z., G.Z. and Z.T. conceived and designed the experiments. X.Z. carried out the experiments and wrote the manuscript. Y.P., Z.L., D.Z. and Z.D. assisted with doing the experiments. Y.L. participated in the statistical analysis. B.Z. and G.Z. and Z.T. revised the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was financially supported by the National Key Research and Development Program of China (Grant No. 2017YFD0101401) and the "Strategic Priority Research Program" of the Chinese Academy of Sciences (Grant No. XDA24030403).

**Acknowledgments:** This work is dedicated to the memory of Baoge Zhu, who devoted his life to soybean breeding. We would like to thank Jingnan Liang (Institute of Microbiology, Chinese Academy of Sciences) for assistance with ultrathin sectioning and transmission electron microscopy.

**Conflicts of Interest:** The authors declare no conflicts of interest.
