Proteomics of Heat-Stress and Ethylene-Mediated Thermotolerance Mechanisms in Tomato Pollen Grains

Abstract

Heat stress is a major cause for yield loss in many crops, including vegetable crops. Even short waves of high temperature, becoming more frequent during recent years, can be detrimental. Pollen development is most heat-sensitive, being the main cause for reduced productivity under heat-stress across a wide range of crops. The molecular mechanisms involved in pollen heat-stress response and thermotolerance are however, not fully understood. Recently, we have demonstrated that ethylene, a gaseous plant hormone, plays a role in tomato (Solanum lycopersicum) pollen thermotolerance. These results were substantiated in the current work showing that increasing ethylene levels by using an ethylene-releasing substance, ethephon, prior to heat-stress exposure, increased pollen quality. A proteomic approach was undertaken, to unravel the mechanisms underlying pollen heat-stress response and ethylene-mediated pollen thermotolerance in developing pollen grains. Proteins were extracted and analyzed by means of a gel LC-MS fractionation protocol, and a total of 1,355 proteins were identified. A dataset of 721 proteins, detected in three biological replicates of at least one of the applied treatments, was used for all analyses. Quantitative analysis was performed based on peptide count. The analysis revealed that heat-stress affected the developmental program of pollen, including protein homeostasis (components of the translational and degradation machinery), carbohydrate, and energy metabolism. Ethephon-pre-treatment shifted the heat-stressed pollen proteome closer to the proteome under non-stressful conditions, namely, by showing higher abundance of proteins involved in protein synthesis, degradation, tricarboxylic acid cycle, and RNA regulation. Furthermore, up-regulation of protective mechanisms against oxidative stress was observed following ethephon-treatment (including higher abundance of glutathione-disulfide reductase, glutaredoxin, and protein disulfide isomerase). Taken together, the findings identified systemic and fundamental components of pollen thermotolerance, and serve as a valuable quantitative protein database for further research.

Heat stress during flowering in cereals – effects and adaptation strategies

“…Although, ROS scavenging is key to ensure that heat stress does not damage the sensitive reproductive tissue, ROS‐dependent programmed cell death is essential for successful fertilisation (Suzuki & Katano, ). Some thermo‐protectants including primary metabolites and phyto‐hormones such as ‐aminobutyric acid (mungbean ( Vigna radiate ), Priya et al , ); salicylic acid (rice, Feng et al , ); flavonols (tomato, Muhlemann et al , ); auxin (rice, Zhang et al , ); and ethylene (tomato, Jegadeesan et al , ) continue to be effective in alleviating heat stress damage in pollen. Although, there are no studies in this direction involving pistils per se , a plausible hypothesis would be that the above‐mentioned compounds will have a similar alleviation potential in pistils exposed to heat stress (Box 2).…”

Identification and Characterization of Contrasting Genotypes/Cultivars for Developing Heat Tolerance in Agricultural Crops: Current Status and Prospects

“…Various proteins such as HSP, those related to anti-oxidant mechanism, and glycolysis were involved in adaption of grape to heat stress as revealed through iTRAQ analysis (Liu et al, 2014). Proteomics analysis of ethylene pre-treated tomato pollen by LC-MS/MS suggested that various proteins help in protecting pollen development and function through higher abundance of protein synthesis and upregulating stress protecting proteins that maintain cellular redox state under heat stress (Jegadeesan et al, 2018). Proteomics analysis by 2-DE technique allowed identification of important heat shock proteins viz., HSP26, HSP16.9, and unknown HSP/Chaperonin contributing to heat stress tolerance in maize (Abou-Deif et al, 2019).…”

Transcriptome and translatome changes in germinated pollen under heat stress uncover roles of transporter genes involved in pollen tube growth

“…Molecular studies have uncovered heat responses in pollen subjected to high temperature similar to other plant cell types including the heat shock response, the unfolded ER protein response or the formation of reactive oxygen species (20). In addition, a number of untargeted transcriptomics, metabolomics, and proteomics studies have been performed to characterize the response of pollen under heat stress conditions at the molecular level (21)(22)(23)(24). However, the limitations of the proteomics and metabolomics technologies compared to highresolution approaches based on next generation sequencing of nucleic acids (NGS) techniques (25), qualify these NGS approaches as very appropriate to gain deeper insight in the response of pollen to heat stress conditions.…”