Some Like it HOT: Protecting Plants from Heat Stress

Seedlings grown at 22ºC for 12 days are healthy and green, but even a short exposure to high temperatures (38–45ºC) can lead to death. WT: normal plants; hot1–3: mutant in a chaperone; hot3–1: mutant in a factor important for protein synthesis (see text).

Plant cells: not your average egg white

We are all familiar with the physical properties of egg whites: as heat rises in the pan, the clear gel turns white and solid. Heat causes the proteins in egg whites to unwind and lose their normal structures, and forces linkages between neighboring proteins.

What happens in the pan should happen to the inside of a plant cell every day when exposed to the heat of the sun; except it does not. Why? That’s because plants produce new proteins during and after heat stress that help them cope. A new study by E. Vierling and colleagues (2017) illustrates just how important new protein synthesis is to plant survival when facing high temperatures.

Chaperones keep proteins at bay

During heat stress, proteins called chaperones prevent other proteins from sticking to each other, just like chaperones at a high school dance keep a watchful eye on teenagers. The absence of chaperones can have dire consequences, including poor growth and death (Hong and Vierling, 2000).

Rebuilding after heat stress

After exposure to high temperatures, plants need to replace or rebuild protein complexes that were damaged by excessive heat. Again, chaperones play an important role. They can, to some extent, reverse the effects of heat stress on proteins. Yes, it’s true: they can (within limits) turn a solid egg white back into a clear gel.

The science behind the findings

Zhang et al. (2017) set out to understand how plants respond to heat stress by measuring protein synthesis during and after exposure to high temperatures in Arabidopsis seedlings, a mustard relative and a great model system for plant biology research. They compared their results to the levels of protein synthesis in a specific mutant, called hot3, that the laboratory had isolated based on its inability to cope with heat stress.

They found that the hot3 mutant recovers from heat stress much more slowly than normal plants, because protein synthesis is much lower for ~10% of proteins. At high temperatures, the mutant happens to inactivate a protein that plays an important role in protein synthesis. A delay of 6–12 hours in recovery of protein synthesis is in fact responsible for most of the mutant’s sensitivity to heat stress.

Crop yield and global rise in temperature: not a pretty picture

Consider this: it takes energy to make new proteins, and plants must decide constantly whether to invest this energy in new leaves and seeds, or in rebuilding existing structures damaged by heat. Recent climate change trends already have measurable effects on food production. A recent study showed that for every one degree-Celsius increase in global temperatures, global yields for the staple crops wheat, rice, corn and soybean drop between three and seven percent (Zhao et al., 2017).

These results highlight the critical role of protein synthesis as a protective and corrective mechanism following stress, and give new directions to help foster a new generation of crops with higher resistance to changes in temperature for agriculture.

Patrice A. Salomé

Department of Chemistry and Biochemistry

University of California, Los Angeles

salome@chem.ucla.edu

ORCID: 0000–0003–4452–9064

Read the research paper on which this story is based:

Zhang, L., Liu, X., Gaikwad, K., Kou, X., Wang, F., Tian, X., Xin, M., Ni, Z., Sun, Q., Peng, H., and Vierling, E. (2017). Mutations in eIF5B confer thermosensitive and pleiotropic phenotypes via translation defects in Arabidopsis thaliana. Plant Cell Published August 14, 2017. DOI: https://doi.org/10.1105/tpc.16.00808.

Other cited references:

Hong, S.W., and Vierling, E. (2000). Mutants of Arabidopsis thaliana defective in the acquisition of tolerance to high temperature stress. Proc. Natl. Acad. Sci. USA 97: 4392–4397.

Zhao C, Liu B, Piao S, Wang X, Lobell DB, Huang Y, Huang M1, Yao Y, Bassu S, Ciais P, Durand JL, Elliott J, Ewert F, Janssens IA, Li T, Lin E, Liu Q, Martre P, Müller C, Peng S, Peñuelas J, Ruane AC, Wallach D, Wang T, Wu D, Liu Z, Zhu Y, Zhu Z, Asseng S., (2017). Temperature increase reduces global yields of major crops in four independent estimates. Proc. Natl. Acad. Sci. USA 114: 9326- 9331.