Abstract
Phytocystatins (PhyCys) comprise a group of inhibitors for cysteine proteinases in plants. They play a wide range of important roles in regulating endogenous processes and protecting plants against various environmental stresses, but the underlying mechanisms remain largely unknown. Here, we detailed the biological functions of MpCYS4, a member of cystatin genes isolated from Malus prunifolia. This gene was activated under water deficit, heat (40°C), exogenous abscisic acid (ABA), or methyl viologen (MV) (Tan et al., 2014a). At cellular level, MpCYS4 protein was found to be localized in the nucleus, cytoplasm, and plasma membrane of onion epidermal cells. Recombinant MpCYS4 cystatin expressed in Escherichia coli was purified and it exhibited cysteine protease inhibitor activity. Transgenic overexpression of MpCYS4 in Arabidopsis (Arabidopsis thaliana) and apple (Malus domestica) led to ABA hypersensitivity and series of ABA-associated phenotypes, such as enhanced ABA-induced stomatal closing, altered expression of many ABA/stress-responsive genes, and enhanced drought tolerance. Taken together, our results demonstrate that MpCYS4 is involved in ABA-mediated stress signal transduction and confers drought tolerance at least in part by enhancing stomatal closure and up-regulating the transcriptional levels of ABA- and drought-related genes. These findings provide new insights into the molecular mechanisms by which phytocystatins influence plant growth, development, and tolerance to stress.
Highlights
Cysteine proteinase inhibitors have been identified in many eukaryotes and extensively studied in insects and mammals (Rawlings et al, 2008)
We report that MpCYS4, GenBank Accession No KF477275, original name MdCYS21, a stress-responsive cystatin gene isolated from M. prunifolia, acts as a positive regulator in drought stress responses, and its function may be due, at least partly, to its interaction within stress-responsive abscisic acid (ABA) signaling transduction that mediates stomatal regulation and a variety of ABA/stressrelated genes expression to cope with drought conditions
We previously demonstrated that MpCYS4 is up-regulated by drought, heat, exogenous ABA, or methyl viologen (MV) treatments in leaves of M. prunifolia (Tan et al, 2014a)
Summary
Cysteine proteinase inhibitors (cystatins) have been identified in many eukaryotes and extensively studied in insects and mammals (Rawlings et al, 2008). MpCYS4 Confers Drought Stress Tolerance in regulating the activity of endogenous cysteine proteinases during a variety of physiological processes, including plant growth and development, the reserves mobilization in seeds and tubers, programmed cell death, and senescence (Belenghi et al, 2003; Martinez et al, 2009; Weeda et al, 2009; Díaz-Mendoza et al, 2014). We previously identified 26 putative PhyCys genes within the entire apple genome and monitored their transcription patterns in the roots, stems, leaves, flowers, and seeds as well as in response to drought, low temperature (4◦C), heat (40◦C), ABA, and oxidative stress (Tan et al, 2014a) Their biological roles had not yet been systematically evaluated. We report that MpCYS4, GenBank Accession No KF477275, original name MdCYS21, a stress-responsive cystatin gene isolated from M. prunifolia, acts as a positive regulator in drought stress responses, and its function may be due, at least partly, to its interaction within stress-responsive ABA signaling transduction that mediates stomatal regulation and a variety of ABA/stressrelated genes expression to cope with drought conditions
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