Overexpression of PtrbHLH, a basic helix-loop-helix transcription factor from Poncirus trifoliata, confers enhanced cold tolerance in pummelo (Citrus grandis) by modulation of H2O2 level via regulating a CAT gene

Abstract

The basic helix-loop-helix (bHLH) family of transcription factors (TFs) plays a crucial role in regulating plant response to abiotic stress by targeting a large spectrum of stress-responsive genes. However, the physiological mechanisms underlying the TF-mediated stress response are still poorly understood for most of the bHLH genes. In this study, transgenic pummelo (Citrus grandis) plants overexpressing PtrbHLH, a TF previously identified from Poncirus trifoliata, were generated via Agrobacterium-mediated transformation. In comparison with the wild-type plants, the transgenic lines exhibited significantly lower electrolyte leakage and malondialdehyde content after cold treatment, thereby resulting in a more tolerant phenotype. Meanwhile, the transgenic lines accumulated dramatically lower reactive oxygen species (ROS) levels, consistent with elevated activity and expression levels of antioxidant enzymes (genes), including catalase (CAT), peroxidase and superoxide dismutase. In addition, PtrbHLH was shown to specifically bind to and activate the promoter of PtrCAT gene. Taken together, these results demonstrated that overexpression of PtrbHLH leads to enhanced cold tolerance in transgenic pummelo, which may be due, at least partly, to modulation of ROS levels by regulating the CAT gene.

Systematic analysis of the basic/helix-loop-helix (bHLH) transcription factor family in pummelo (Citrus grandis) and identification of the key members involved in the response to iron deficiency

“…These studies have provided us a comprehensive understanding of potential gene functions and have promoted related research progress. However, no such study has been done on the citrus bHLH family, except that Geng and Liu (2018) [45] identified 56 putative bHLH genes from sweet orange. In this study, we used a genomewide approach to identify 128 CgbHLHs from pummelo.…”

“…To date, only very limited citrus bHLH genes have been functionally characterized, including PtrbHLH, an ortholog of AtbHLH33 (ICE2), that was isolated from trifoliate orange (Poncirus trifoliata) and proved to confer cold tolerance by regulating both POD-and CATmediated reactive oxygen species (ROS) scavenging [29,45]. CsbHLH18 of sweet orange was also proved to modulate cold tolerance and ROS homeostasis [51].…”

Systematic analysis of the basic/helix-loop-helix (bHLH) transcription factor family in pummelo (Citrus grandis) and identification of the key members involved in the response to iron deficiency

“…The first type, such as CgbHLH3, CgbHLH6, These studies have provided us a comprehensive understanding of potential gene functions and have promoted related research progress. However, no such study has been done on the citrus bHLH family, except that Geng and Liu (2018) [45] identified 56 putative bHLH genes from sweet orange. In this study, we used a genome-wide approach to identify 128 CgbHLHs from pummelo.…”

Systematic analysis of the basic/helix-loop-helix (bHLH) transcription factor family in pummelo (Citrus grandis) and identification of the key members involved in the response to iron deficiency

“…Except for eight genes were still undetectable, the other 34 genes were determined to be up- These studies have provided us a comprehensive understanding of potential gene functions and have promoted related research progress. However, no such study has been done on the citrus bHLH family, except that Geng and Liu (2018) [44] identified 56 putative bHLH genes from sweet orange. In this study, we used a genome-wide approach to identify 128 CgbHLHs from pummelo.…”

“…To date, only very limited citrus bHLH genes have been functionally characterized, including PtrbHLH, an ortholog of AtbHLH33 (ICE2), that was isolated from trifoliate orange (Poncirus trifoliata) and proved to confer cold tolerance by regulating both POD-and CAT-mediated reactive oxygen species (ROS) scavenging [25,44]. CsbHLH18 of sweet orange was also proved to modulate cold tolerance and ROS homeostasis [50].…”