Abstract
BackgroundReactive oxygen species (ROS) play a prominent role in signal transduction and cellular homeostasis in plants. However, imbalances between generation and elimination of ROS can give rise to oxidative stress in growing cells. Because ROS are important to cell growth, ROS modulation could be responsive to natural or human-mediated selection pressure in plants. To study the evolution of oxidative stress related genes in a single plant cell, we conducted comparative expression profiling analyses of the elongated seed trichomes ("fibers") of cotton (Gossypium), using a phylogenetic approach.ResultsWe measured expression changes during diploid progenitor species divergence, allopolyploid formation and parallel domestication of diploid and allopolyploid species, using a microarray platform that interrogates 42,429 unigenes. The distribution of differentially expressed genes in progenitor diploid species revealed significant up-regulation of ROS scavenging and potential signaling processes in domesticated G. arboreum. Similarly, in two independently domesticated allopolyploid species (G. barbadense and G. hirsutum) antioxidant genes were substantially up-regulated in comparison to antecedent wild forms. In contrast, analyses of three wild allopolyploid species indicate that genomic merger and ancient allopolyploid formation had no significant influences on regulation of ROS related genes. Remarkably, many of the ROS-related processes diagnosed as possible targets of selection were shared among diploid and allopolyploid cultigens, but involved different sets of antioxidant genes.ConclusionOur data suggests that parallel human selection for enhanced fiber growth in several geographically widely dispersed species of domesticated cotton resulted in similar and overlapping metabolic transformations of the manner in which cellular redox levels have become modulated.
Highlights
Reactive oxygen species (ROS) play a prominent role in signal transduction and cellular homeostasis in plants
The role of ROS has been studied in cell wall biosynthesis, where ROS have been shown to be involved in lignin biosynthesis, crosslinking reactions between cell wall components, and loosening of cell walls in growing tissues [18,19,20,21,22]
Exogenous H2O2 levels are regulated by redox status-related antioxidant enzymes including Cu/ Zn-superoxide dismutase (CSD) that localizes to secondary cell walls of developing cotton fibers and is involved in cell wall growth [22]
Summary
Reactive oxygen species (ROS) play a prominent role in signal transduction and cellular homeostasis in plants. In addition to the necessity of controlling excess potentially damaging ROS, eukaryotes have harnessed ROS as signaling molecules for a diverse array of regulatory processes, including responses to abiotic and biotic stresses, regulation of growth and development, and control of programmed cell death [2,3,4,5,9,10,11] Because of their important roles as signaling molecules, as well as their toxicity at higher levels, ROS concentrations are finely tuned and developmentally regulated by a complex gene network (at least 152 genes in Arabidopsis; [2]), which collectively control and modulate ROS metabolism [2,5]. Redox levels in cotton fiber cells are important for stability of cellulose synthases, necessary for cellulose biosynthesis during fiber elongation and secondary wall formation [30]
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