Abstract:
Plants reprogram gene expression as an adaptive response to survive high temperatures.
While the identity and functions of intracellular heat stress-responsive proteins have been extensively
studied, the heat response of proteins secreted to the extracellular matrix is unknown. Here,
we used Sorghum bicolor, a species adapted for growth in hot climates, to investigate the extracellular
heat-induced responses. When exposed to 40 ◦C for 72 h, heat-sensitive Arabidopsis cell suspension
cultures died, while ICSB338 sorghum cell cultures survived by activation of a transcriptional
response characterized by the induction of HSP70 and HSP90 genes. Quantitative proteomic
analysis of proteins recovered from cell culture medium revealed specific heat stress-induced protein
accumulation within the sorghum secretome. Of the 265 secreted proteins identified, 31 responded to
heat (≥2-fold change), with 84% possessing a predicted signal peptide for targeting to the classical
secretory pathway. The differentially accumulated proteins have putative functions in metabolism,
detoxification, and protein modifications. A germin (SORBI_3003G427700) was highly heat-inducible
at both protein and gene level. Overall, our study reveals new insights into sorghum responses to
heat and provides a useful resource of extracellular proteins that could serve as targets for developing
thermotolerant crops. Data are available via ProteomeXchange with identifier PXD021536.
