Exploring the mechanism of maintaining heat acclimation memory mediated by the HSP101-HSA32 module in Arabidopsis

S. MITRA, N. Y. LIU, S. J. YU, H.Y. LI, Y. Y. SHEN, Y. Y. CHARNG

Agricultural Biotechnology Research Center, Academia Sinica, Taipei, Taiwan

Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan

Heat acclimation memory (HAM) helps plants to cope with recurring heat stress. The interplay between the molecular chaperone HSP101 and Heat-Stress-Associated 32 kDa protein (HSA32) maintains HAM at the protein level. A unique relationship between HSP101-HSA32 sustains the memory of heat stress for a few days after the stress-free period conferring more durable acquired thermotolerance. The precise mechanism remains unclear. Here, we focused on how HSP101 regulates HSA32 in Arabidopsis. We observed that the interplay between HSP101 and HSA32 was not restricted to specific temperatures. HSA32 was degraded through proteasome and autophagy pathways in absence and presence of HSP101, respectively. The TurboID technique was employed to identify components interacting with HSA32. HSP101 was one of the targets, suggesting a direct interaction exists. After heat acclimation, HSA32-GFP formed speckles in root cells with or without HSP101. However, these speckles disappeared faster in the presence of HSP101, suggesting HSP101 remodels the conformation of HSA32. To identify the features of conformational change, the intrinsic disorder region predicted in AtHSA32 was deleted or site-directed mutagenized; both variants became less stable. Thus, we conclude that HSP101 retards the proteasome-mediated degradation of HSA32 by triggering a conformational change through protein-protein interaction for HAM maintenance.