Arabidopsis Stromal 70-kD Heat Shock Proteins Are Essential for Plant Development and Important for Thermotolerance of Germinating Seeds      

Abstract

The 70-kD heat shock proteins (Hsp70s) have been shown to be important for protein folding, protein translocation, and stress responses in almost all organisms and in almost all subcellular compartments. However, the function of plastid stromal Hsp70s in higher plants is still uncertain. Genomic surveys have revealed that there are two putative stromal Hsp70s in Arabidopsis thaliana, denoted cpHsc70-1 (At4g24280) and cpHsc70-2 (At5g49910). In this study, we show that cpHsc70-1 and cpHsc70-2 could indeed be imported into the chloroplast stroma. Their corresponding T-DNA insertion knockout mutants were isolated and designated as Dcphsc70-1 and Dcphsc70-2. No visible phenotype was observed in the Dcphsc70-2 mutant under normal growth conditions. In contrast, Dcphsc70-1 mutant plants exhibited variegated cotyledons, malformed leaves, growth retardation, and impaired root growth, even though the protein level of cpHsc70-2 was up-regulated in the Dcphsc70-1 mutant. After heat shock treatment of germinating seeds, root growth from Dcphsc70-1 seeds was further impaired, indicating that cpHsc70-1 is important for thermotolerance of germinating seeds. No Dcphsc70-1 Dcphsc70-2 double mutant could be obtained, suggesting that the Dcphsc70 double knockout was lethal. Genotype analyses of F 1 seedlings from various crosses indicated that double-knockout mutation was lethal to the female gametes and reduced the transmission efficiency of the male gametes. These results indicate that cpHsc70s are essential for plant development and the two cpHsc70s most likely have redundant but also distinct functions.

Heat-shock dependent oligomeric status alters the function of a plant-specific thioredoxin-like protein, AtTDX

“…5C), the transgenic lines overexpressing the native or C304/307S mutant AtTDX rapidly recovered during the poststress recovery period. The observation is in good agreement with the results of Arabidopsis stromal HSP70 (24). In contrast, almost all of the WT plants and the suppression lines were unable to recover from the damage caused by heat shock (Fig.…”

Alternative Processing of Arabidopsis Hsp70 Precursors during Protein Import into Chloroplasts

“…40) In chloroplasts, the T-DNA knockout mutant of AtHsp70-6 exhibited severe phenotypic alterations as compared with AtHsp70-7. 34) As we have shown here the presence of two mature forms of Athsp70-6 might indicate a different role for AtHsp70-7. Thus an assumption can be made that the m2 form of AtHsp70-6 should have a function distinct from the m1 forms of AtHsp70-6 and AtHsp70-7, but it is unclear exactly which mature form, m1AtHsp70-6 or m2AtHSp70-6, causes the effect on phenotype alteration.…”

Proteomic Analysis of Chloroplast-to-Chromoplast Transition in Tomato Reveals Metabolic Shifts Coupled with Disrupted Thylakoid Biogenesis Machinery and Elevated Energy-Production Components

“…Another heat shock protein, HSC70-2 (Solyc11g020040), highly expressed in the tomato plastids, increases continuously. It has been described as essential for plant development in Arabidopsis (Su and Li, 2008). Its role in chromoplast differentiation would deserve elucidation.…”