Mulberry (Morus alba), a widely distributed economic plant, can withstand long-term flooding stress. However, the regulatory gene network underlying this tolerance is unknown. In the present study, mulberry plants were subjected to submergence stress. Subsequently, mulberry leaves were collected to perform quantitative reverse-transcription PCR (qRT-PCR) and transcriptome analysis. Genes encoding ascorbate peroxidase and glutathione S-transferase were significantly upregulated after submergence stress, indicating that they could protect the mulberry plant from flood damage by mediating ROS homeostasis. Genes that regulate starch and sucrose metabolism; genes encoding pyruvate kinase, alcohol dehydrogenase, and pyruvate decarboxylase (enzymes involved in glycolysis and ethanol fermentation); and genes encoding malate dehydrogenase and ATPase (enzymes involved in the TCA cycle) were also obviously upregulated. Hence, these genes likely played a key role in mitigating energy shortage during flooding stress. In addition, genes associated with ethylene, cytokinin, abscisic acid, and MAPK signaling; genes involved in phenylpropanoid biosynthesis; and transcription factor genes also showed upregulation under flooding stress in mulberry plants. These results provide further insights into the adaptation mechanisms and genetics of submergence tolerance in mulberry plants and could aid in the molecular breeding of these plants.

BGLUs (β-glucosidase) are members of the glycoside hydrolase family 1 (GH1) and play essential roles in plant growth, development, and responses to environmental stresses. Although extensive genome-wide studies of BGLU gene families have been conducted in numerous plant species, the BGLU gene family in Morus alba has not been systematically characterized. In this study, 41 MaBGLU genes were identified from the M. alba genome and their biological characteristics were analyzed using bioinformatics approaches. The MaBGLU proteins exhibited considerable variation in physicochemical properties and were classified into eight mulberry-specific subfamilies based on the Arabidopsis thaliana classification system. Sequence alignment revealed conserved core motifs among MaBGLU proteins, along with broadly similar exon-intron organization. Chromosomal mapping showed that the 41 MaBGLU genes were unevenly distributed across nine chromosomes, with six tandem duplication events involving 30 genes and one segmental duplication detected. Promoter analysis identified numerous cis-acting elements associated with stress and hormone responses. Expression analysis of nine MaBGLU genes under abiotic stress and hormone treatments revealed distinct expression patterns, underscoring the important roles of MaBGLU genes in abiotic stress adaptation and hormone signaling pathways. This study provides a comprehensive foundation for understanding the functions of β-glucosidases in woody plants and identifies promising candidate genes for stress-tolerance breeding in M. alba.

Alcohol dehydrogenase (ADH) is a key enzyme for ethanol fermentation under anaerobiosis and is vital for plant growth, development, and abiotic stress tolerance. Although the (MDR)-ADH gene family in Morus has not been systematically characterized, this study performs a genome-wide analysis to investigate its evolution and flooding-responsive transcription patterns. In this study, a comprehensive genome-wide bioinformatic analysis of the Morus alba (MDR)-ADH (MaADH) gene family, including physicochemical characteristics, evolutionary relationships, subcellular localization, gene structural organization, cis-regulatory element composition, and interspecific syntenic relationships, was conducted. A total of 20 MaADH genes were identified from the M. alba genome, and all encoded proteins contained the conserved GroES-like alcohol dehydrogenase N-terminal domain (ADH_N) and zinc-binding alcohol dehydrogenase domain (ADH_zinc_N). Phylogenetic analysis grouped these genes into six evolutionary clades. The identified MaADH genes showed an uneven chromosomal distribution across seven chromosomes. Moreover, qRT-PCR analysis of 11 selected MaADH genes showed that most genes are significantly upregulated in the roots and stems under flooding conditions, with a characteristic temporal expression pattern of initial induction followed by attenuation. These results suggest that the differentially expressed MaADH genes may participate in the transcriptional response to flooding stress in M. alba. These results will contribute to further research on the biological function of the MaADH candidates and provide new candidate genes for breeding programs focused on the flood response of M. alba.