Some like it hot, some like it warm: phenotyping to explore thermotolerance diversity

Abstract

Plants have evolved overlapping but distinct cellular responses to different aspects of high temperature stress. These responses include basal thermotolerance, short- and long-term acquired thermotolerance, and thermotolerance to moderately high temperatures. This 'thermotolerance diversity' means that multiple phenotypic assays are essential for fully describing the functions of genes involved in heat stress responses. A large number of genes with potential roles in heat stress responses have been identified using genetic screens and genome wide expression studies. We examine the range of phenotypic assays that have been used to characterize thermotolerance phenotypes in both Arabidopsis and crop plants. Three major variables differentiate thermotolerance assays: (1) the heat stress regime used, (2) the developmental stage of the plants being studied, and (3) the actual phenotype which is scored. Consideration of these variables will be essential for deepening our understanding of the molecular genetics of plant thermotolerance.

Fig. 1. Heat stress regimes used for thermotolerance phenotyping in Arabidopsis

A. Schemes of heat stress regimes for four major types of thermotolerance: basal thermotolerance (BT), short-term acquired thermotolerance (SAT), long-term acquired thermotolerance (LAT), and thermotolerance to moderately high temperatures (TMHT). The schemes show temperatures that are often used in young seedlings. The temperature and duration of treatment varies depending on the exact tissue tested or experimental design used. The dashed lines indicate the time-lag between the applied temperature and the sample temperature, which vary with the heating device used. The output traits are assessed after various periods of incubation after the heat treatment. B. The heat stress regime for gradient acclimation is adopted from [31].