A Heat Shock Transcription Factor TrHSFB2a of White Clover Negatively Regulates Drought, Heat and Salt Stress Tolerance in Transgenic Arabidopsis

Abstract

Heat shock transcription factors (HSF) are divided into classes A, B and C. Class A transcription factors are generally recognized as transcriptional activators, while functional characterization of class B and C heat shock transcription factors have not been fully developed in most plant species. We isolated and characterized a novel HSF transcription factor gene, TrHSFB2a (a class B HSF) gene, from the drought stress-sensitive forage crop species, white clover (Trifolium repens). TrHSFB2a was highly homologous to MtHSFB2b, CarHSFB2a, AtHSFB2b and AtHSFB2a. The expression of TrHSFB2a was strongly induced by drought (PEG6000 15% w/v), high temperature (35 °C) and salt stresses (200 mM L−1 NaCl) in white clover, while subcellular localization analysis showed that it is a nuclear protein. Overexpression of the white clover gene TrHSFB2a in Arabidopsis significantly reduced fresh and dry weight, relative water contents (RWC), maximum photosynthesis efficiency (Fv/Fm) and performance index on the absorption basis (PIABS), while it promoted leaf senescence, relative electrical conductivity (REC) and the contents of malondialdehyde (MDA) compared to a wild type under drought, heat and salt stress conditions of Arabidopsis plants. The silencing of its native homolog (AtHSFB2a) by RNA interference in Arabidopsis thaliana showed opposite trends by significantly increasing fresh and dry weights, RWC, maximum photosynthesis efficiency (Fv/Fm) and performance index on the absorption basis (PIABS) and reducing REC and MDA contents under drought, heat and salt stress conditions compared to wild type Arabidopsis plants. These phenotypic and physiological indicators suggested that the TrHSFB2a of white clover functions as a negative regulator of heat, salt and drought tolerance. The bioinformatics analysis showed that TrHSFB2a contained the core B3 repression domain (BRD) that has been reported as a repressor activator domain in other plant species that might repress the activation of the heat shock-inducible genes required in the stress tolerance process in plants. The present study explores one of the potential causes of drought and heat sensitivity in white clover that can be overcome to some extent by silencing the TrHSFB2a gene in white clover.

Rapid Identification of High-Temperature Responsive Genes Using Large-Scale Yeast Functional Screening System in Potato

“…Plants share common regulatory signals or pathways in response to abiotic stresses such as high temperature, drought, and high salt [22,23]. Among the 1931 high temperature responsive genes we screened, more than half responded to both drought and high salt stress simultaneously (Table S3).…”

Deciphering the roles of unknown/uncharacterized genes in plant development and stress responses

“…Furthermore, a novel gene DUF569 (AT1G69890) with "domain of unknown function" positively regulates drought stress in Arabidopsis (Nabi et al, 2021). The HSF transcription factor gene TrHSFB2a (B-type HSF), which was recently identified in drought-sensitive white clover (Trifolium repens), negatively regulates drought resistance (Iqbal et al, 2022) (Figure 3B). Under drought stress conditions, overexpression of the ONAC066 gene (a novel gene whose function has been newly determined) enhances the tolerance of rice to drought stress and sensitivity to ABA (Yuan et al, 2019).…”

“…TrHSFB2a expression in white clover was strongly induced by exposure to high temperature (35°C) and the encoded protein negatively regulates heat tolerance (Iqbal et al, 2022). The POFs in Arabidopsis enhance plant tolerance to oxidative stress under both cold and heat stress (Luhua et al, 2008) (Figure 3C).…”

Characterization of the Heat Shock Transcription Factor Family in Lycoris radiata and Its Potential Roles in Response to Abiotic Stresses

“…Furthermore, it has been demonstrated that HSF members are markedly associated with plant development and various stress responses, such as responses to freezing and salt, drought, and high-temperature tolerance [ 5 , 7 , 22 , 23 , 24 , 25 , 26 ]. In plants, HSF genes are the primary modulator of high-temperature stress [ 22 ].…”