Genome-wide Identification and Expression Analysis of the Malate Dehydrogenase Gene Family in Gossypium Arboreum

Malate dehydrogenase (MDH) is a key enzyme that catalyzes the reversible oxidation of malate to oxaloacetate and plays a crucial role in various cellular processes, such as cell expansion, wall thickening and cell elongation. Although individual genes belonging to MDH gene family have been partially identified in various plants, there have been no reports of a genome-wide characterization of the MDH gene family in cotton. Here, we identified a total of 13 MDH genes from the genome of a diploid cotton Gossypium arboreum and designated GaMDH1-13 based on their chromosomal locations. These MDH members were unevenly distributed on 8 of the13 chromosomes. Segmental duplications that played a dominant role in the expansion of the MDH gene family were estimated to have occurred between 19.07 to 20.47 million years ago (MYA), when a recent large-scale genome duplication occurred in cotton. Phylogenetic analyses showed that the putative MDH proteins formed five groups (I to V) in plant species. GaMDH genes within the same group shared similar gene structures and domain constitutions. Furthermore, expression analysis showed that the GaMDH genes were differentially expressed in root, stem, leaf, hypocotyl, petal and anther, with higher expression levels detected during different fiber developmental stages. Notably, GaMDH13 had the highest expression level during the fast fiber elongation stage that ranged from 5 to 15 day post-anthesis (DPA), suggesting that the MDH gene plays a vital role in fiber development. The results of this study will aid functional analyses of the MDH genes in cotton fiber development.