Comparative Genome-Wide Analysis of the Malate Dehydrogenase Gene Families in Cotton

Malate dehydrogenases (MDHs) play crucial roles in the physiological processes of plant growth and development. In this study, 13 and 25 MDH genes were identified from Gossypium raimondii and Gossypium hirsutum, respectively. Using these and 13 previously reported Gossypium arboretum MDH genes, a comparative molecular analysis between identified MDH genes from G. raimondii, G. hirsutum, and G. arboretum was performed. 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. An analysis of chromosomal localization suggested that segmental duplication played a major role in the expansion of cotton MDH gene families. Additionally, a selective pressure analysis indicated that 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, suggesting the functional diversification of these genes in cotton growth and fiber development. Finally, a promoter analysis indicated redundant but typical cis-regulatory elements for the potential functions and stress activity of many MDH genes. This study provides fundamental information for a better understanding of cotton MDH gene families and aids in functional analyses of the MDH genes in cotton fiber development

Regulation of proline accumulation and its molecular and physiological functions in stress defence

The accumulation of proline is a conserved response of plants to abiotic stress conditions. Moreover, the activation of proline metabolism takes place during the plant response to some pathogens. Although these responses are well documented, the molecular and physiological functions of proline accumulation under stress are still a matter of debate. The biochemical pathways that lead to proline accumulation and its functions in regulating development are described in the cognate chapter “Proline Metabolism and its Functions in Development”. In this chapter, we will describe the potential roles assigned to proline accumulation, dissecting the data coming from in vitro/in silico and in vivo approaches, and those coming from bacterial or unicellular eukaryotes and plants. With this, we aim to present a clear view of the evidence related to the molecular and physiological functions of proline accumulation under stress conditions in plants. In recent years, the understanding of the regulation of proline accumulation at transcriptional level under stress conditions in plants has been increased considerably, yet little is known about the possible occurrence of post-translational regulatory mechanisms. We will integrate this knowledge with the potential roles of proline accumulation to see whether it contributes to comprehending which roles might be physiologically more relevant