AtHsfA2 modulates expression of stress responsive genes and enhances tolerance to heat and oxidative stress in Arabidopsis

In nature, plants are subject to changes of tempera-ture. Thus, like other organisms, plants have evolved strategies for preventing damage caused by rapid changes in temperature and for repairing what damage is unavoidable. Heat stress responses have been well documented in a wide range of organisms. In all spe-cies studied, the heat shock (HS) response is charac-terized by a rapid production and a transient accumu-lation of specific families of proteins known as heat shock proteins (Hsps) th…     

Functional analysis of the Hikeshi-like protein and its interaction with HSP70 in Arabidopsis

Heat shock proteins (HSPs) refold damaged proteins and are an essential component of the heat shock response. Previously, the 70 kDa heat shock protein (HSP70) has been reported to translocate into the nucleus in a heat-dependent manner in many organisms. In humans, the heat-induced translocation of HSP70 requires the nuclear carrier protein Hikeshi. In the Arabidopsis genome, only one gene encodes a protein with high homology to Hikeshi, and we named this homolog Hikeshi-like (HKL) protein. In this study, we show that two Arabidopsis HSP70 isoforms accumulate in the nucleus in response to heat shock and that HKL interacts with these HSP70s. Our histochemical analysis revealed that HKL is predominantly expressed in meristematic tissues, suggesting the potential importance of HKL during cell division in Arabidopsis. In addition, we show that HKL regulates HSP70 localization, and HKL overexpression conferred thermotolerance to transgenic Arabidopsis plants. Our results suggest that HKL plays a positive role in the thermotolerance of Arabidopsis plants and cooperatively interacts with HSP70.     

Serine/threonine protein phosphatase 5 (PP5) interacts with substrate under heat stress conditions and forms protein complex in Arabidopsis

Protein phosphatase 5 plays a pivotal role in signal transduction in animal and plant cells, and it was previously shown that Arabidopsis protein phosphatase 5 (AtPP5) performs multiple enzymatic activities that are mediated by conformational changes induced by heat shock stress. In addition, transgenic overexpression of AtPP5 gene conferred enhanced heat shock resistance compared with wild-type plant. However, the molecular mechanism underlying this enhanced heat shock tolerance through functional and conformational changes upon heat stress is not clear. In this report, AtPP5 was shown to preferentially interact with its substrate, MDH, under heat stress conditions. In addition, in co-IP analysis, AtPP5 was observed to form a complex with AtHsp90 in Arabidopsis. These results suggest that AtPP5 may enhance thermotolerance via forming multi-chaperone complexes under heat shock conditions in Arabidopsis. Finally, we show that AtPP5 is primarily localized in the cytoplasm of Arabidopsis.     

An Arabidopsis heat shock protein complements a thermotolerance defect in yeast.

The heat shock protein Hsp104 of the yeast Saccharomyces cerevisiae plays a key role in promoting survival at extreme temperatures. We found that when diverse higher plant species are exposed to high temperatures they accumulate proteins that are antigenically related to Hsp104. We isolated a cDNA corresponding to one of these proteins from Arabidopsis. The protein, AtHSP101, is 43% identical to yeast Hsp104. DNA gel blot analysis indicated that AtHSP101 is encoded by a single- or low-copy number gene. AtHsp101 mRNA was undetectable in the absence of stress but accumulated to high levels during exposure to high temperatures. When AtHSP101 was expressed in yeast, it complemented the thermotolerance defect caused by a deletion of the HSP104 gene. The ability of AtHSP101 to protect yeast from severe heat stress strongly suggests that this HSP plays an important role in thermotolerance in higher plants.     

Heat stress phenotypes of Arabidopsis mutants implicate multiple signaling pathways in the acquisition of thermotolerance

To investigate the importance of different processes to heat stress tolerance, 45 Arabidopsis (Arabidopsis thaliana) mutants and one transgenic line were tested for basal and acquired thermotolerance at different stages of growth. Plants tested were defective in signaling pathways (abscisic acid, salicylic acid, ethylene, and oxidative burst signaling) and in reactive oxygen metabolism (ascorbic acid or glutathione production, catalase) or had previously been found to have temperature-related phenotypes (e.g. fatty acid desaturase mutants, uvh6). Mutants were assessed for thermotolerance defects in seed germination, hypocotyl elongation, root growth, and seedling survival. To assess oxidative damage and alterations in the heat shock response, thiobarbituric acid reactive substances, heat shock protein 101, and small heat shock protein levels were determined. Fifteen mutants showed significant phenotypes. Abscisic acid (ABA) signaling mutants (abi1 and abi2) and the UV-sensitive mutant, uvh6, showed the strongest defects in acquired thermotolerance of root growth and seedling survival. Mutations in nicotinamide adenine dinucleotide phosphate oxidase homolog genes (atrbohB and D), ABA biosynthesis mutants (aba1, aba2, and aba3), and NahG transgenic lines (salicylic acid deficient) showed weaker defects. Ethylene signaling mutants (ein2 and etr1) and reactive oxygen metabolism mutants (vtc1, vtc2, npq1, and cad2) were more defective in basal than acquired thermotolerance, especially under high light. All mutants accumulated wild-type levels of heat shock protein 101 and small heat shock proteins. These data indicate that, separate from heat shock protein induction, ABA, active oxygen species, and salicylic acid pathways are involved in acquired thermotolerance and that UVH6 plays a significant role in temperature responses in addition to its role in UV stress.     

AtsHsp17.6-CⅠ和AtsHsp17.6-CⅡ基因对非生物胁迫的应答研究

小分子热激蛋白是植物受到热胁迫后的主要表达产物之一,与植物细胞耐热有密切关系。该研究发现,拟南芥小分子热激蛋白基因AtsHsp17.6-CⅠ和AtsHsp17.6-CⅡ 除热激之外,重金属离子Ni⁺、Pb²⁺、Cu²⁺、Zn²⁺和Al³⁺均能诱导这2个热激蛋白基因的表达;氧化胁迫和渗透胁迫同样也能诱导它们表达。该研究将由CaMV35S启动子驱动的这2个小分子热激蛋白基因导入拟南芥,RT-PCR分析表明,2个小分子热激蛋白基因在转基因植物中呈现组成型表达。实验结果表明,组成型表达小分子热激蛋白基因AtsHsp17.6-CⅠ的转基因植物表现出对6 μmol·L^-1 Cd²⁺胁迫、0.4% NaCl胁迫的耐受性。研究表明,这2个小分子热激蛋白基因可能参与着多种抗逆途径,推测其能够减轻或抵抗逆境胁迫引起的伤害并对其进行修复。     

The Arabidopsis J-protein AtDjB1 facilitates thermotolerance by protecting cells against heat-induced oxidative damage

AtDjB1 belongs to the J-protein family in Arabidopsis thaliana. Its biological functions in plants are largely unknown. In this study, we examined the roles of AtDjB1 in resisting heat and oxidative stresses in A. thaliana using reverse genetic analysis. AtDjB1 knockout plants (atj1-1) were more sensitive to heat stress than wildtype plants, and displayed decreased concentrations of ascorbate (ASC), and increased concentrations of hydrogen peroxide (H(2)O(2)) and oxidative products after heat shock. Application of H(2)O(2) accelerated cell death and decreased seedling viability in atj1-1. Exogenous ASC conferred much greater thermotolerance in atj1-1 than in wildtype plants, suggesting that a lower concentration of ASC in atj1-1 could be responsible for the increased concentration of H(2)O(2) and decreased thermotolerance. Furthermore, AtDjB1 was found to localize to mitochondria, directly interact with a mitochondrial heat-shock protein 70 (mtHSC70-1), and stimulate ATPase activity of mtHSC70-1. AtDjB1 knockout led to the accumulation of cellular ATP and decreased seedling respiration, indicating that AtDjB1 modulated the ASC concentration probably through affecting the function of mitochondria. Taken together, these results suggest that AtDjB1 plays a crucial role in maintaining redox homeostasis, and facilitates thermotolerance by protecting cells against heat-induced oxidative damage.     

Heat-tolerant basmati rice engineered by over-expression of hsp101

Rice is sensitive to high-temperature stress at almost all the stages of its growth and development. Considering the crucial role of heat shock protein 101 (Hsp101) in imparting thermotolerance to cells, we introduced Arabidopsis thaliana hsp101 (Athsp101) cDNA into the Pusa basmati 1 cultivar of rice (Oryza sativa L.) by Agrobacterium-mediated transformation. Stable integration and expression of the transgene into the rice genome was demonstrated by Southern, northern and western blot analyses. There appeared no adverse effect of over-expression of the transgene on overall growth and development of transformants. The genetic analysis of tested T₁ lines showed that the transgene segregated in a Mendelian fashion. We compared the survival of T₂ transgenic lines after exposure to different levels of high-temperature stress with the untransformed control plants. The transgenic rice lines showed significantly better growth performance in the recovery phase following the stress. This thermotolerance advantage appeared to be solely due to over-expression of Hsp101 as neither the expression of low-molecular-weight heat shock proteins (HSPs) nor of other members of Clp family proteins was altered in the transgenic rice. The production of high temperature tolerant transgenic rice cultivars would provide a stability advantage under supra-optimal temperature regime thereby improving its overall performance.     

Neighbour signals perceived by phytochrome B increase thermotolerance in Arabidopsis

Due to the preeminence of reductionist approaches, understanding of plant responses to combined stresses is limited. We speculated that light‐quality signals of neighbouring vegetation might increase susceptibility to heat shocks because shade reduces tissue temperature and hence the likeness of heat shocks. In contrast, plants of Arabidopsis thaliana grown under low‐red/far‐red ratios typical of shade were less damaged by heat stress than plants grown under simulated sunlight. Neighbour signals reduce the activity of phytochrome B (phyB), increasing the abundance of PHYTOCHROME‐INTERACTING FACTORS (PIFs). The phyB mutant showed high tolerance to heat stress even under simulated sunlight, and a pif multiple mutant showed low tolerance under simulated shade. phyB and red/far‐red ratio had no effects on seedlings acclimated with nonstressful warm temperatures before the heat shock. The phyB mutant showed reduced expression of several fatty acid desaturase (FAD) genes and less proportion of fully unsaturated fatty acids and electrolyte leakage of membranes exposed to heat shocks. Red‐light‐activated phyB also reduced thermotolerance of dark‐grown seedlings but not via changes in FADs expression and membrane stability. We propose that the reduced photosynthetic capacity linked to thermotolerant membranes would be less costly under shade, where the light input limits photosynthesis.