β-glucosidase BG3Contributes To Drought Tolerance In Arabidopsis Thaliana

The phytohormone ABA plays important roles in responsing to environmental stress conditions suchas drought, cold and high salt stress during the plant life cycle. ABA also plays a very important role in theprocess of plant development including germination process, dormancy and plant regeneration, etc.Plants adapting to the environmental conditions rely on cellular ABA levels which are deteremined bytwo processes: catabolic and biosynthetic pathways reduce and increase ABA levels, respectively. Multiplecatabolic pathways reduce cellular ABA levels. For instance, ABA is degraded by hydroxylation in onestrategy and is conjugated with Glc to produce inactive ABA-GE in another. ABA levels are increased bythree different biosynthetic strategies. One involves the de novo biosynthesis of ABA. The second strategyinvolves the one-step hydrolysis of Glc-conjugated ABA （ABA-GE） by a β-glucosidase homolog,Arabidopsis thaliana BG1. The third biosynthetic strategy involves the one-step hydrolysis ofGlc-conjugated ABA （ABA-GE） by a β-glucosidase homolog, Arabidopsis thaliana BG2. However, howmany different β-glucosidase proteins produce ABA from ABA-GE is still unknown.In present study, we isolated T-DNA insertion homozygous mutant bg3of β-glucosidase family inArabidopsis. We found that bg3mutant had higher water loss rate than wild type. Stomatal behavioranalysis showed that stomata of bg3tending to open wider than that of WT under stress. In addition, WTshowed stronger drought-tolerance than bg3mutant.Determination of ABA content in plants under drought condition, showed that bg3hold lower ABAcontent than that of WT, while under normal condition there no difference in ABA level between bg3andWT. In additon, the expression of BG3was induced by sereval abiotic stress. GUS staining analysis of BG3gene tissue-specific expression showed that this gene is transcript in various tissue, including roots, stems,leaves, flowers, especially in mature conducting tissue. These results suggest that BG3may have thefunction of hydrolysis ABA-GE and release of free ABA to enhance stress-tolerance response of plants aswell as BG1and BG2.Fluorescence localization result of pHBT::BG3::GFP fusion proteins using transient expression inprotoplast of mesophyll cells, showed BG3enzyme protein localized in cytoplast. In order to study BG3function on protein level, we screened and identified BG3:: MYC transgenic plants, and provide genetic material for subsequent studyThis study provides a basis for researching the role of β-glucosidase enzymes in the plant inresponsing to abiotic stress and identifying the component which participate in regulating ABA level.