AtbHLH68 transcription factor contributes to the regulation of ABA homeostasis and drought stress tolerance in Arabidopsis thaliana

Abstract

Basic helix-loop-helix (bHLH) transcription factors are involved in a wide range of developmental processes and in response to biotic and abiotic stresses. They represent one of the biggest families of transcription factors but only few of them have been functionally characterized. Here we report the characterization of AtbHLH68 and show that, although the knock out mutant did not have an obvious development phenotype, it was slightly more sensitive to drought stress than the Col-0, and AtbHLH68 overexpressing lines displayed defects in lateral root (LR) formation and a significant increased tolerance to drought stress, likely related to an enhanced sensitivity to abscisic acid (ABA) and/or increased ABA content. AtbHLH68 was expressed in the vascular system of Arabidopsis and its expression was modulated by exogenously applied ABA in an organ-specific manner. We showed that the expression of genes involved in ABA metabolism [AtAAO3 (AtALDEHYDE OXIDASE 3) and AtCYP707A3 (AtABSCISIC ACID 8'HYDROXYLASE 3)], in ABA-related response to drought-stress (AtMYC2, AtbHLH122 and AtRD29A) or during LRs development (AtMYC2 and AtABI3) was de-regulated in the overexpressing lines. We propose that AtbHLH68 has a function in the regulation of LR elongation, and in the response to drought stress, likely through an ABA-dependent pathway by regulating directly or indirectly components of ABA signaling and/or metabolism.

Genome-wide analysis of basic helix-loop-helix (bHLH) transcription factors in Brachypodium distachyon

“…Subgroup IX bHLHs were proposed to be involved in photoperiodism flowering (FBH1-FBH4) [ 183 ] and facilitate stomatal opening through phosphorylation (AKS2) [ 184 ]. Two studied X proteins (bHLH068 and bHLH112) could response to abiotic stresses [ 185 , 186 ]. Subgroup XI members in Arabidopsis (LRL1-LRL5) [ 130 , 187 , 188 ] and rice (OsRHL1) [ 189 ] regulate root hair development, while another protein OsPTF1 is involved in phosphate starvation tolerance [ 190 ].…”

Revisiting the Role of Plant Transcription Factors in the Battle against Abiotic Stress

“…The bHLH (basic helix-loop-helix) transcription factors constitute the second largest family in angiosperms and are universally distributed in all eukaryotic organisms [ 43 ]. The highly conserved bHLH signature domain comprises two distinct functional regions, a basic N-terminal DNA-binding region, and a helix-loop-helix region involved in protein–protein interactions via the formation of homo- and heterodimeric complexes located at the C-terminal end, which is a prerequisite for TF function [ 119 , 120 ].…”

“…Similarly, accumulating evidence has indicated that bHLH TFs also participate in regulating various abiotic stresses. For example, the expression of AtbHLH68 , a putative non-DNA-binding bHLH gene, was altered in Arabidopsis in an organ-specific manner with exogenous application of ABA, and its overexpression conferred transgenic plants significant drought resistance, likely via regulation of ABA homeostasis [ 43 ]. Further, AtbHLH112 overexpressors displayed better ROS-scavenging abilities, as well as elevated levels of proline that led to high resistance against multiple abiotic stresses, including salt and drought [ 45 ].…”

Expression of Pumpkin CmbHLH87 Gene Improves Powdery Mildew Resistance in Tobacco

“…Recent studies have indicated that a number of bHLH transcription factor genes are involved in responses to abiotic stresses including drought, salt, and cold. The overexpression of AtbHLH068 and OsbHLH148 in transgenic Arabidopsis thaliana and rice, respectively, reportedly induces drought stress tolerance via abscisic acid (ABA)-and jasmonic acid (JA)-mediated signaling pathways (Seo et al, 2011;Le Hir et al, 2017). In rice, OsbHLH062, OsJAZ9, and OsNINJA form a transcriptional regulatory complex that fine-tunes the expression of JA-responsive genes involved in salt stress tolerance (e.g., OsHAK21) (Wu et al, 2015).…”