Abstract
Proline metabolism is important for environmental responses, plant growth, and development. However, its precise roles in plant abiotic stress tolerance are not well understood. Mutants are valuable for the identification of new genes and for elucidating their roles in physiological mechanisms. We applied a suppressor mutation approach to identify novel genes involved in the regulation of proline metabolism in Arabidopsis. Using the atrzf1 (Arabidopsis thaliana ring zinc finger 1) mutant as a parental line for activation tagging mutagenesis, we selected several mutants with suppressed induction of proline accumulation under dehydration conditions. One of the selected mutants [proline content alterative 22 (pca22)] appeared to have reduced proline contents compared with the atrzf1 mutant under drought stress. Generally, pca22 mutant plants displayed suppressed atrzf1 insensitivity to dehydration and abscisic acid during early seedling growth. Additionally, the pca22 mutant exhibited shorter pollen tube length than wild-type (WT) and atrzf1 plants. Furthermore, PCA22-overexpressing plants were more sensitive to dehydration stress than the WT and RNAi lines. Green fluorescent protein-tagged PCA22 was localized to the cytoplasm of transgenic Arabidopsis cells. Collectively, these results suggest that pca22 acts as dominant suppressor mutant of atrzf1 in the abiotic stress response.
Highlights
Proline (Pro) is a multifunctional amino acid in plants, and Pro accumulation has been reported to occur in response to drought, high salinity, heavy metals, pathogen infection, low temperature, and oxidative stress (Verbruggen and Hermans, 2008; Yang et al, 2009; Szabados and Savouré, 2010)
Because atrzf1 is known to hyperaccumulate Pro in response to water deficit conditions (Ju et al, 2013), the activation-tagged T1 population was screened for decreased Pro concentration to drought stress compared with the atrzf1 mutant. atrzf1 mutants were transformed with Agrobacterium harboring the binary vector pSKI015, which contained four copies of the Cauliflower mosaic virus (CaMV) 35S enhancer at the right border of the T-DNA and a BAR (Bialaphos resistance) gene as a selectable marker (Weigel et al, 2000)
These results suggest that pca22 participates in the suppression of Pro production in atrzf1 mutants under drought conditions
Summary
Proline (Pro) is a multifunctional amino acid in plants, and Pro accumulation has been reported to occur in response to drought, high salinity, heavy metals, pathogen infection, low temperature, and oxidative stress (Verbruggen and Hermans, 2008; Yang et al, 2009; Szabados and Savouré, 2010). Pro accumulation is believed to play adaptive roles in plant stress tolerance. Pro has been proposed to act as a compatible solute and a source of nitrogen and carbon storage (Hare and Cress, 1997). Pro has been proposed to function as a molecular chaperone to stabilize the structure of proteins, and as a regulator of cellular redox potential, and an antioxidant controlling free radical levels (Hare et al, 1999). Ju et al (2013) reported that Pro accumulation is regulated by ubiquitination during abiotic stress. Pro accumulation may be part of the stress signal influencing the adaptive response (Maggio et al, 2002)
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