**1. Introduction**

*Hibiscus hamabo* Sieb.et Zucc. (*H. hamabo*) is a deciduous shrub native to the coastlines of Korea, Japan, and China that is currently considered an endangered plant in the Zhejiang Province of China [1–3]. As a semi-mangrove species, it is adaptable to pronounced changes in ecological characteristics in land–sea transitions [2,4], with a strong adaptability to saline alkali soil [5]. Therefore, *H. hamabo* plays an important role in the improvement of saline–alkali lands and has been widely applied in the afforestation of coastal beaches in environmental governance efforts in recent years [5]. *H. hamabo* is an excellent material for the study of plant salt tolerance. At present, studies on salt tolerance in *H. hamabo* have mainly been based on morphological observations: investigations of the physiological and molecular mechanisms involved [6–9]. Previously, we presented the genome sequencing of *H. hamabo* using PacBio, Illumina, and Hi-C sequencing technology and analyzed its salt tolerance mechanism based on genome and transcriptome data [2].

The MYB transcription factor family is one of the largest in plants and plays key roles in the regulation of plant growth and stress [10,11]. MYB family members have highly conserved domains forming three α-helices in three-dimensional space [10]. The second and third helices form a "helix-turn-helix" structure with a hydrophobic core containing three tryptophan residues, which is the DNA binding site [10]. According to the number of adjacent imperfect repeats, MYB genes can be divided into four gene subfamilies, namely 1R-MYB, 2R-MYB, 3R-MYB, and 4R-MYB [12].

MYB transcription factors have been reported to alleviate or eliminate plant stressrelated damage through their signal transduction network, which regulates targeted genes to initiate physiological and biochemical responses [13,14]. Abscisic acid (ABA) and salt can induce transcription levels of *AmMYB1*, and the overexpression of *AmMYB1* in tobacco

**Citation:** Liu, D.; Gu, C.; Fu, Z.; Wang, Z. Genome-Wide Identification and Analysis of *MYB* Transcription Factor Family in *Hibiscus hamabo*. *Plants* **2023**, *12*, 1429. https://doi.org/10.3390/ plants12071429

Academic Editor: Rebecca Grumet

Received: 29 January 2023 Revised: 18 March 2023 Accepted: 20 March 2023 Published: 23 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

<sup>1</sup> Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing 210014, China

improves the tolerance to salt stress [15]. Overexpression of the wheat R2R3-MYB gene members *TaMYB32*, *TaMYB33*, *TaMYB56-B*, and *TaMYB73* in *Arabidopsis thaliana* (*A. thaliana*) significantly improved salt tolerance [11]. All the genome data of *A. thaliana* provided the possibility for the description and classification of the MYB gene family in plants [16]. Since then, scientists have identified the MYB family from different species and clarified their biological function and that of related genes by molecular biological and other means [12,17,18]. In this study, all MYB genes detected in the genome of *H. hamabo* and their chromosomal distribution, phylogenetic relationships, gene structural organization, and protein motif content were analyzed. Furthermore, their expression in response to stress stimuli was analyzed using previously published transcriptomic data of *H. hamabo*, which was validated for selected MYB members by comparative RT-qPCR. This work provides a preliminary framework for the identification of candidate MYB genes mediating stress responses, especially to salt stress in *H. hamabo*. The candidate genes identified could be useful both in future studies of the underlying mechanisms of salt tolerance in *H. hamabo* and as potential markers in subsequent *H. hamabo* breeding.
