What Did We Learn From Current Progress in Heat Stress Tolerance in Plants? Can Microbes Be a Solution?

Abstract

Temperature is a significant parameter in agriculture since it controls seed germination and plant growth. Global warming has resulted in an irregular rise in temperature posing a serious threat to the agricultural production around the world. A slight increase in temperature acts as stress and exert an overall negative impact on different developmental stages including plant phenology, development, cellular activities, gene expression, anatomical features, the functional and structural orientation of leaves, twigs, roots, and shoots. These impacts ultimately decrease the biomass, affect reproductive process, decrease flowering and fruiting and significant yield losses. Plants have inherent mechanisms to cope with different stressors including heat which may vary depending upon the type of plant species, duration and degree of the heat stress. Plants initially adapt avoidance and then tolerance strategies to combat heat stress. The tolerance pathway involves ion transporter, osmoprotectants, antioxidants, heat shock protein which help the plants to survive under heat stress. To develop heat-tolerant plants using above-mentioned strategies requires a lot of time, expertise, and resources. On contrary, plant growth-promoting rhizobacteria (PGPRs) is a cost-effective, time-saving, and user-friendly approach to support and enhance agricultural production under a range of environmental conditions including stresses. PGPR produce and regulate various phytohormones, enzymes, and metabolites that help plant to maintain growth under heat stress. They form biofilm, decrease abscisic acid, stimulate root development, enhance heat shock proteins, deamination of ACC enzyme, and nutrient availability especially nitrogen and phosphorous. Despite extensive work done on plant heat stress tolerance in general, very few comprehensive reviews are available on the subject especially the role of microbes for plant heat tolerance. This article reviews the current studies on the retaliation, adaptation, and tolerance to heat stress at the cellular, organellar, and whole plant levels, explains different approaches, and sheds light on how microbes can help to induce heat stress tolerance in plants.

Acute and chronic impacts of heat stress on planetary health

“…Plant growth-promoting rhizobacteria form biofilm, stimulate root development, enhance HSPs and nutrient availability, especially nitrogen and phosphorous, and produce and regulate various phytohormones, enzymes, and metabolites that help plants to maintain growth under heat stress. 56 Anti-inflammatory cytokines also play a role in responses to heat stress. Interactions between HSPs, cytokines, and endotoxins are thought to orchestrate responses to heat injury.…”

“…Seeds treated with the microbes Bacillus amyloliquefaciens and Azospirillum brasilense had decreased ROS under heat stress. Plant growth‐promoting rhizobacteria form biofilm, stimulate root development, enhance HSPs and nutrient availability, especially nitrogen and phosphorous, and produce and regulate various phytohormones, enzymes, and metabolites that help plants to maintain growth under heat stress 56 …”

Application of ethanol alleviates heat damage to leaf growth and yield in tomato

“…Heat stress damages plant growth and yield ( Hoshikawa et al., 2021 ; Ahmad et al., 2022 ). Extensive research has elucidated how photosynthesis is highly sensitive to heat stress ( Hu et al., 2020 ).…”

Landscape of biomolecular condensates in heat stress responses

“…Heat stress is defined as exposure to elevated temperatures above a certain threshold for a sufficient amount of time to cause irreversible harmful effects in plants at the morphological, biochemical, and physiological levels ( Wahid et al., 2007 ). Heat stress impairs several growth stages and metabolic processes at the cellular level, ultimately leading to a loss of yield quantity/quality or death ( Bita and Gerats, 2013 ; Ahmad et al., 2022 ).…”

“…At the morphological and physiological levels, heat stress causes several types of damage, such as inhibition of shoot and root growth, leaf senescence, leaf scorching and sunburn, fruit damage (discoloration), changes in osmotic pressure, decreased photosynthesis, hormonal changes, and other injuries ( Hu et al., 2020 ; Ahmad et al., 2022 ). Researchers have always been interested in how plants perceive heat at the molecular level and translate this stress into functional cellular signals.…”