Heat shock response in Arabidopsis Hsa32 knockout mutant

Plants and animals share similar mechanisms in the heat-shock (HS) response, such as synthesis of the conserved HS proteins (Hsps). However, because plants are confined to a growing environment, in general they require unique features to cope with heat stress. We have analyzed the function of a novel Hsp, heat-stress-associated 32-kD protein (Hsa32), which is highly conserved in land plants but absent in most other organisms. The gene responds to HS at the transcriptional level in moss, Arabidopsis, and rice. Like other Hsps, Hsa32 protein accumulates greatly in Arabidopsis seedlings after HS treatment. Disruption of Hsa32 by T-DNA insertion does not affect growth and development under normal conditions. However, the acquired thermotolerance in the knockout line was compromised following a long recovery period (> 24 h) after an acclimation HS treatment, when a severe HS challenge killed the mutant but not the wild-type plants, but no significant difference was observed if they were challenged within a short recovery period. Microarray analysis of the knockout mutant indicates that only the expression of Hsa32 was significantly altered in HS response. Taken together, our results suggest that Hsa32 is not required for the induction but maintenance of acquired thermotolerance. This report provides direct evidence that a plant-specific Hsp plays an important role in thermotolerance. Keywords: heat shock response Total RNA was isolated from the shoots of 15-d old wild-type and Hsa32 knockout mutant seedlings (a pool of about 100 plants per treatment in duplicates) harvested immediately after treatment at 37C (HS) or 22C (control) for 2 h. In this experiment, total eight chips were used, 1 each for 2 biological replicates of the control and HS-treated samples for the wild type and mutant plants.