**Genome-Wide Analysis of Multiple Organellar RNA Editing Factor Family in Poplar Reveals Evolution and Roles in Drought Stress**

**Dongli Wang 1,†, Sen Meng 1,2,†, Wanlong Su <sup>1</sup> , Yu Bao <sup>1</sup> , Yingying Lu <sup>1</sup> , Weilun Yin <sup>1</sup> , Chao Liu 1,\* and Xinli Xia 1,\***


Received: 22 January 2019; Accepted: 18 March 2019; Published: 21 March 2019

**Abstract:** Poplar (Populus) is one of the most important woody plants worldwide. Drought, a primary abiotic stress, seriously affects poplar growth and development. Multiple organellar RNA editing factor (*MORF*) genes—pivotal factors in the RNA editosome in *Arabidopsis thaliana*—are indispensable for the regulation of various physiological processes, including organelle C-to-U RNA editing and plasmid development, as well as in the response to stresses. Although the poplar genome sequence has been released, little is known about *MORF* genes in poplar, especially those involved in the response to drought stress at the genome-wide level. In this study, we identified nine *MORF* genes in the Populus genome. Based on the structural features of MORF proteins and the topology of the phylogenetic tree, the *P. trichocarpa* (Ptr) MORF family members were classified into six groups (Groups I–VI). A microsynteny analysis indicated that two (22.2%) *PtrMORF* genes were tandemly duplicated and seven genes (77.8%) were segmentally duplicated. Based on the *dN/d<sup>S</sup>* ratios, purifying selection likely played a major role in the evolution of this family and contributed to functional divergence among *PtrMORF* genes. Moreover, analysis of qRT-PCR data revealed that *PtrMORFs* exhibited tissue- and treatment-specific expression patterns. *PtrMORF* genes in all group were involved in the stress response. These results provide a solid foundation for further analyses of the functions and molecular evolution of *MORF* genes in poplar, and, in particular, for improving the drought resistance of poplar by genetics manipulation.

**Keywords:** *Populus trichocarpa*; multiple organellar RNA editing factor; drought stress; RNA editing; genome
