Molecular Identification And Characterization Of Cotton Malate Dehydrogenase Gene Family

Malate dehydrogenase(MDH,EC 1.1.1.37)belongs to the A group of dehydrogenases,which constitute a gene family of NAD(P)~+-dependent conserved enzymes that catalyzes the reversible oxidation of oxaloacetate to malate.However,malate is very important metabolic intermediate in a plant cell,having a variety of biological functions for metabolic pathways of glyoxylate bypass,tricarboxylic acid cycle,glucogenesis,synthesis of amino acid,and reduction/oxidation stability.To date,little is known about MDH gene family in cotton.In this study,we carried out a genome-wide identification and comparative analysis of cotton MDH gene family and revealed the composition of this family in cotton genomes as well as the expression features during different growth periods of fiber development,which could provide a foundation for functions studies of this gene family in the development of cotton fiber cells.In total,51 MDH genes were identified in Gossypium raimondii,Gossypium arboretum and Gossypium hirsutum genomes.Based on multiple sequence alignments,cotton MDHs were divided into five subgroups:mitochondrial MDH,peroxisomal MDH,plastidial MDH,chloroplastic MDH and cytoplasmic MDH.Almost all of the MDHs within the same subgroup shared similar gene structure,amino acid sequence,and conserved motifs in their functional domains.The examination of chromosomal localization suggested that 10 segmental duplication events played a major role in the expansion of cotton MDH gene families and purifying selection acted as a vital force in the evolution of MDH gene families in cotton.Meanwhile,an expression analysis showed the distinct expression profiles of GhMDHs in different vegetative tissues and at different fiber developmental stages.For instance,the transcripts of GhcMDH1 were prominently detected in 5~25 days post anthesis(DPA)fibers and highly abundant at 15DPA fibers,suggesting the functional diversification of these genes in cotton growth and fiber development.Finally,we isolated a cytosolic malate dehydrogenase gene preferentially expressed in cotton fibers,designated as GhcMDH1,from G.hirsutum and explored its expression feature,subcellular location and possible molecular function in cotton fiber development for the first time.The cloned cDNA of GhcMDH1 is 1520 base pairs in length,which encoding for 332 amino acid residues.Sequence alignment showed that the deduced amino acid sequence of GhcMDH1 protein shared a high similarity to other plant cMDHs.Confocal and immunological analysis confirmed that GhcMDH1 protein was subcellularly localized to the cytosol.Quantitative real-time PCR and enzymatic activity determination analyses revealed that the transcripts of GhcMDH1,total activity and malate content of cotton fibers were positively correlated with the fiber elongation rates,suggesting that GhcMDH1 may function in malate synthesis in fast fiber elongation.In conclusion,this study provides fundamental information for a better understanding of the distribution,evolution and expression of cotton MDH gene families in cotton genomes,which could renders valuable insights to further investigate the MDH genes in cotton fiber development.