Heat Stress Responses and Thermotolerance in Maize

Abstract

High temperatures causing heat stress disturb cellular homeostasis and impede growth and development in plants. Extensive agricultural losses are attributed to heat stress, often in combination with other stresses. Plants have evolved a variety of responses to heat stress to minimize damage and to protect themselves from further stress. A narrow temperature window separates growth from heat stress, and the range of temperatures conferring optimal growth often overlap with those producing heat stress. Heat stress induces a cytoplasmic heat stress response (HSR) in which heat shock transcription factors (HSFs) activate a constellation of genes encoding heat shock proteins (HSPs). Heat stress also induces the endoplasmic reticulum (ER)-localized unfolded protein response (UPR), which activates transcription factors that upregulate a different family of stress response genes. Heat stress also activates hormone responses and alternative RNA splicing, all of which may contribute to thermotolerance. Heat stress is often studied by subjecting plants to step increases in temperatures; however, more recent studies have demonstrated that heat shock responses occur under simulated field conditions in which temperatures are slowly ramped up to more moderate temperatures. Heat stress responses, assessed at a molecular level, could be used as traits for plant breeders to select for thermotolerance.

Role of Reactive Oxygen Species and Hormones in Plant Responses to Temperature Changes

“…Davletova et al (2005) also showed, using knockout (KO) mutants of cytosolic ascorbate peroxidase, an ROS scavenging enzyme and that heat shock transcription factor 21 (HSF21/AtHSFA4) is involved in H 2 O 2 stress sensing, suggesting a close link between the HSF and ROS [65]. A few other major ROS responsive TFs include MYB domain protein 44 (MYB44), Heat Stress transcription factor A-4A (HSFA4A), and Ethylene Responsive Element-Binding Factor 6 (ERF6) [53,[67][68][69][70][71]. Similarly, heat stress induction has been shown to trigger the expression of heat shock proteins HSP17.6 and HSP18.2 in Arabidopsis cell cultures.…”

Heat Stress After Pollination Reduces Kernel Number in Maize by Insufficient Assimilates

“…Maize tassels (male flowers) growing at the top of the plant were found to be vulnerable to low-level heat stress and this affected pollen viability (Dong et al, 2021;Wang et al, 2021). At the flowering stage, high temperatures inhibited anther dehiscence, pollen viability, and pollen germination, which caused kernel abortion and maize yield reduction (Carberry et al, 1989;Bakhtavar et al, 2015;Hatfield and Prueger, 2015;Li and Howell, 2021;Wang et al, 2021). Additionally, high temperatures caused a delay in the anthesis-silking interval (ASI) of maize, resulting in reduced kernel number, although plenty of pollen was still present (Wang et al, 2019).…”

Coordination of RNA Processing Regulation by Signal Transduction Pathways

“…Moreover, DNAJC17 depletion induced widespread changes in AS of endogenous genes in HeLa cells. These findings uncovered a novel role for DNAJC17 in splicing-related processes and suggest that splicing impairment may contribute to its essential function in early development [166].…”

“…More recently, a role in splicing regulation was also described for DNAJC17, a member of the HSP40 family [166]. DNAJC17 is an essential protein that was identified as a susceptibility factor for congenital hypothyroidism and myeloproliferative disorders.…”