The BAG2 and BAG6 Genes Are Involved in Multiple Abiotic Stress Tolerances in Arabidopsis Thaliana

Abstract

The BAG proteins are a family of multi-functional co-chaperones. In plants, BAG proteins were found to play roles both in abiotic and biotic stress tolerance. However, the function of Arabidopsis BAG2 remains largely unknown, whereas BAG6 is required for plants’ defense to pathogens, although it remains unknown whether BAG6 is involved in plants’ tolerance to abiotic stresses. Here, we show that both BAG2 and BAG6 are expressed in various tissues and are upregulated by salt, mannitol, and heat treatments and by stress-related hormones including ABA, ethylene, and SA. Germination of bag2, bag6 and bag2 bag6 seeds is less sensitive to ABA compared to the wild type (WT), whereas BAG2 and BAG6 overexpression lines are hypersensitive to ABA. bag2, bag6, and bag2 bag6 plants show higher survival rates than WT in drought treatment but display lower survival rates in heat-stress treatment. Consistently, these mutants showed differential expression of several stress- and ABA-related genes such as RD29A, RD29B, NCED3 and ABI4 compared to the WT. Furthermore, these mutants exhibit lower levels of ROS after drought and ABA treatment but higher ROS accumulation after heat treatment than the WT. These results suggest that BAG2 and BAG6 are negatively involved in drought stress but play a positive role in heat stress in Arabidopsis.

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“…In our data, the pattern of most SlBAGs expression during salt and osmotic stress is similar (Fig. 4 ) and is in accordance with prior AtBAG studies 11 , 15 , 31 , however the possibility of osmotic shock using 200 mM NaCl cannot be neglected therefore long-term salt treatment assays with gradual NaCl application instead of single step application might provide a clearer picture of SlBAGs expression under salt stress 35 .…”

“…4 ). Several previous studies suggest the significant upregulation of AtBAG6 and AtBAG7 and down regulation of AtBAG1 and AtBAG4 in heat stress 11 , 15 , 21 , 23 , 31 . We also reported downregulation of SlBAG1 and SlBAG4 at early time points of heat stress, however we did not report any significant diffence in the SlBAG7 expression during heat stress.…”

“…This is in accordance with the previous studies on Arabidopsis BAG genes that also contain stress-responsive elements including ABRE, ERE, CGTCA motif, MBS, TC-rich repeats 11 , 15 . Further, the increased GUS activity driven by AtBAG2 and AtBAG6 promoters in salt and osmotic stress and post ACC and ABA treatment also suggest that these stress related elements are involved in BAG genes regulation during plant stress response 31 . The presence of stress related elements in the BAG promoters could be related to stress specific response of BAG genes as BAG genes from many plants such as Arabidopsis , rice, soya bean and wheat have shown plant stress specific response and have been successfully used for improving stress tolerance in Arabidopsis and rice 27 , 31 – 34 .…”

“…Further, the increased GUS activity driven by AtBAG2 and AtBAG6 promoters in salt and osmotic stress and post ACC and ABA treatment also suggest that these stress related elements are involved in BAG genes regulation during plant stress response 31 . The presence of stress related elements in the BAG promoters could be related to stress specific response of BAG genes as BAG genes from many plants such as Arabidopsis , rice, soya bean and wheat have shown plant stress specific response and have been successfully used for improving stress tolerance in Arabidopsis and rice 27 , 31 – 34 . The potential role of SlBAGs in plant stress response is also supported by their differential expression pattern in abiotic stresses and in response to hormonal treatment (Figs.…”

“…4 ). The Arabidopsis homologues of these genes viz AtBAG2, AtBAG3, AtBAG4, AtBAG6 also showed increased expression in salt stress conditions 11 , 15 , 31 . Moreover, the enhanced expression of OsBAG4 in rice roots and TaBAG2 in wheat in response to saline was also reported indicating the involvement of SlBAGs in salt stress response 32 , 34 .…”