Hsa32 對於阿拉伯芥耐熱功能與機制之研究

Abstract

Novel heat-stress-associated 32-kD protein (Hsa32) is required for the maintenance of acquired thermotolerance (AT) in Arabidopsis. Here, we demonstrate that Hsa32 is required, not only for AT, but also for basal thermotolerance (BT). Severe heat stress (44oC, 23 min) killed hsa32-1 and hsp101 mutants while wild type plants survived. Immunoblot and RT-PCR analysis revealed that plants lacking Hsa32 or Hsp101 displayed delayed post-heat stress (HS) induction of HSP genes. Moreover, blocking the synthesis of HSPs in the wild type plants seedlings following severe HS at appropriate time by cycloheximide decreased the seedlings’ survival rate, suggesting that post-HS response is required for BT. The HsfA2 knockout line also showed a moderately impaired post-HS response and BT suggesting that HsfA2 plays a regulatory role in BT. Plants constitutively expressing Hsa32 tolerated sudden shifts to extreme temperature better than wild type plants. Although Hsa32 accumulated in mature seeds, Hsa32 only moderately affected seed thermotolerance. In previous reports, Hsa32 was suggested to have phosphosulfolactate (PSL) synthase activity due to a weak similarity with PSL synthase from Methanococcus jannaschii. Here, we showed that Hsa32 may not have PSL synthase activity in vitro, and overexpressing homolog of PSL synthase from Corynebacterium glutamicum could not complement the hsa32-1 plants. We conclude that post-HS induction of Hsa32 is required for BT, but PSL synthase activity is not required by Hsa32 for thermal protection in Arabidopsis.