Protein expression changes during cotton fiber elongation in response to low temperature stress

Low temperature stress is one of the major abiotic stresses limiting the formation of cotton (Gossypium hirsutum L.) fiber qualities, especially fiber length. To investigate the molecular adaptation mechanisms of cotton fiber elongation to low temperature stress, two cotton cultivars, Kemian 1 (low temperature-tolerant) and Sumian 15 (low temperature-sensitive), were planted in the field at two sowing dates (25 April and 10 June). The two sowing dates resulted in different growing conditions and the main environmental difference between them was temperature, particularly the mean daily minimum temperature (MDTmin). When the sowing date was delayed, the MDTmin decreased from 26.9 °C (25 April) to 20.6 °C (10 June). Low temperature stress (MDTmin of 20.6 °C) shortened the fiber length significantly in two cultivars, but the decreased extent was larger in Sumian 15 than that in Kemian 1. Proteomic analysis of three developmental stages (10, 15 and 20 days post-anthesis [DPA]) showed that 37 spots changed significantly (p < 0.05) in abundance under low temperature stress and they were identified using mass spectrometry. These proteins were involved in malate metabolism, soluble sugar metabolism, cell wall loosening, cellulose synthesis, cytoskeleton, cellular response, and redox homeostasis. The results suggest that the enhancement of osmoticum maintenance, cell wall loosening, cell wall components biosynthesis, and cytoskeleton homeostasis plays important roles in the tolerance of cotton fibers to low temperature stress. Moreover, low levels of PEPCase, expansin, and ethylene signaling proteins may potentially lead to the low temperature sensitivity of Sumian 15 at the proteomic level.     

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.     

An integrative analysis of four CESA isoforms specific for fiber cellulose production between Gossypium hirsutum and Gossypium barbadense

Cotton fiber is an excellent model system of cellulose biosynthesis; however, it has not been widely studied due to the lack of information about the cellulose synthase (CESA) family of genes in cotton. In this study, we initially identified six full-length CESA genes designated as GhCESA5–GhCESA10. Phylogenetic analysis and gene co-expression profiling revealed that CESA1, CESA2, CESA7, and CESA8 were the major isoforms for secondary cell wall biosynthesis, whereas CESA3, CESA5, CESA6, CESA9, and CESA10 should involve in primary cell wall formation for cotton fiber initiation and elongation. Using integrative analysis of gene expression patterns, CESA protein levels, and cellulose biosynthesis in vivo, we detected that CESA8 could play an enhancing role for rapid and massive cellulose accumulation in Gossypium hirsutum and Gossypium barbadense. We found that CESA2 displayed a major expression in non-fiber tissues and that CESA1, a housekeeping gene like, was predominantly expressed in all tissues. Further, a dynamic alteration was observed in cell wall composition and a significant discrepancy was observed between the cotton species during fiber elongation, suggesting that pectin accumulation and xyloglucan reduction might contribute to cell wall transition. In addition, we discussed that callose synthesis might be regulated in vivo for massive cellulose production during active secondary cell wall biosynthesis in cotton fibers.