# Natural populations of Arabidopsis thaliana differ in seedling responses to high-temperature stress

## TL;DR

Natural Arabidopsis populations differ in how they respond to high heat stress, with Hsp101 levels linked to better survival and root growth.

## Contribution

Identifies adaptive variation in thermotolerance and Hsp101 expression across natural Arabidopsis populations along climate gradients.

## Key findings

- Hsp101 expression correlates with seedling survival and root growth after 45°C heat stress.
- Pre-acclimation increases thermotolerance at 45°C but not at 42°C.
- Thermotolerance and Hsp101 levels are linked to climate variation of the plants' home sites.

## Abstract

Heat stress limits species distribution, especially under predicted global climate change. The research article focuses on identifying the adaptive variation in response to high-temperature stress across an elevation gradient in natural Arabidopsis thaliana populations. We show that the accumulation of Hsp101, an important heat shock protein known to be essential for acquired thermotolerance, was positively associated with seedling survival and post-stress root growth. Pre-acclimation significantly increased thermotolerance at 45°C but not 42°C. Both Hsp101 and thermotolerance were correlated with the climate variation of home sites. Our study contributes to growing knowledge on abiotic stress responses in natural plant populations.

Little is known about adaptive within-species variation in thermotolerance in wild plants despite its likely role in both functional adaptation at range limits and in predicting response to climate change. Heat shock protein Hsp101, rapidly heat induced in Arabidopsis thaliana, plays a central role in thermotolerance in laboratory studies, yet little is known about variation in its expression in natural populations. We explored variation in thermotolerance and Hsp101 expression in seedlings from 16 natural populations of A. thaliana sampled along an elevation and climate gradient. We tested both naive controls (maintained at 22 °C until heat stress) and thermally pre-acclimated plants (exposed to a 38 °C 3-h acclimation treatment). After acclimation, seedlings were exposed to one of two heat stresses: 42 or 45 °C. Thermotolerance was measured as post-stress seedling survival and root growth. When stressed at 45 °C, both thermotolerance and Hsp101 expression were significantly increased by pre-acclimation. However, thermotolerance did not differ between pre-acclimation and control when followed by a 42 °C stress. Immediately after heat stress, pre-acclimated seedlings contained significantly more Hsp101 than control seedlings. At 45 °C, Hsp101 expression was positively associated with survival (r2 = 0.37) and post-stress root growth (r2 = 0.15). Importantly, seedling survival, post-stress root growth at 45 °C and Hsp101 expression at 42 °C were significantly correlated with the home sites' first principal component of climate variation. This climate gradient mainly reflects a temperature and precipitation gradient. Thus, the extent of Hsp101 expression modulation and thermotolerance appear to be interrelated and to evolve adaptively in natural populations of A. thaliana.