Abstract
Monodehydroasorbate reductase (MDHAR) (EC1.6.5.4), a key enzyme in ascorbate-glutathione recycling, plays important roles in cell growth, plant development and physiological response to environmental stress via control of ascorbic acid (AsA)-mediated reduction/oxidation (redox) regulation. Until now, information regarding MDHAR function and regulatory mechanism in Gossypium have been limited. Herein, a genome-wide identification and comprehensive bioinformatic analysis of 36 MDHAR family genes in four Gossypium species, Gossypium arboreum, G. raimondii, G. hirsutum, and G. barbadense, were performed, indicating their close evolutionary relationship. Expression analysis of GhMDHARs in different cotton tissues and under abiotic stress and phytohormone treatment revealed diverse expression features. Fiber-specific expression analysis showed that GhMDHAR1A/D, 3A/D and 4A/D were preferentially expressed in fiber fast elongating stages to reach peak values in 15-DPA fibers, with corresponding coincident observances of MDHAR enzyme activity, AsA content and ascorbic acid/dehydroascorbic acid (AsA/DHA) ratio. Meanwhile, there was a close positive correlation between the increase of AsA content and AsA/DHA ratio catalyzed by MDHAR and fiber elongation development in different fiber-length cotton cultivars, suggesting the potential important function of MDHAR for fiber growth. Following H2O2 stimulation, GhMDHAR demonstrated immediate responses at the levels of mRNA, enzyme, the product of AsA and corresponding AsA/DHA value, and antioxidative activity. These results for the first time provide a comprehensive systemic analysis of the MDHAR gene family in plants and the four cotton species and demonstrate the contribution of MDHAR to fiber elongation development by controlling AsA-recycling-mediated cellular redox homeostasis.
Highlights
The Monodehydroasorbate reductase (MDHAR) were distributed across different chromosomes, with locations on fivechromosomes of G. arboreum (AA genome, Chr 2, 9, 10, 11, and 13) and of G. raimondii (DD genome, Chr 2, 6, 8, 11, and 13)
The results indicated that GhMDHAR1A/D and GhMDHAR3A/D were preferentially expressed in all detected tissues including roots, stems, leaves, petals, stamens, pistils, ovules and fibers, with the most significant accumulations in fiber development, suggesting their potential important roles in tissue development especially in fiber growth (Figure 4A)
These results suggest that these GhMDHAR genes might play important function for fiber development
Summary
Reactive oxygen species (ROS) are important signaling molecules that play significant roles in plant development, cell growth and in response to environmental stresses and phytohormone signaling [1,2,3,4,5]. To counteract excessive ROS and the detrimental effects of cellular oxidation, plants have evolved corresponding defense mechanism for detoxification of ROS by controlling cellular reduction/oxidation (redox) balance. The ascorbate-glutathione (Asc-GSH) cycle, namely Asc recycling pathway, is regarded as the critical pathway that mediates the antioxidative molecule of Asc as a coenzyme 4.0/). It stabilizes cellular redox status to play a multifunction role in controlling cell growth and plant development [6,7]. Of the Asc antioxidant system enzymes, ascorbate peroxidase (APX, EC1.11.1.11) is the prototypical ROS-scavenging enzyme utilizing ascorbic acid (AsA)
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