The involvement of chloroplast HSP100/ClpB in the acquired thermotolerance in tomato

Abstract

The chloroplast HSP100/ClpB is a newly documented member of the ClpB family, but little was known about its role in imparting thermotolerance to cells. A cDNA coding for a HSP100/ClpB homolog has been cloned from Lycopersicon esculentum and termed as Lehsp100/ClpB (the cDNA sequence of Lehsp100/ClpB has been submitted to the GenBank database under accession number: AB219939). The protein encoded by the cDNA was most similar to the putative chloroplast HSP100/ClpBs in higher plants and the ClpB from Cyanobacterium Synechococcus sp. A 97 kDa protein, which matched the predicted size of mature LeHSP100/ClpB, was immunologically detected in chloroplast isolated from heat-treated tomato plants. In addition, the fusion protein, combining the transit sequence of LeHSP100/ClpB and GFP, was found to be located in chloroplast based on the observations of fluorescent microscope images. These results indicated the chloroplast-localization of LeHSP100/ClpB. Both the transcript and the protein of Lehsp100/ClpB were not detected under normal growth conditions, but they were induced by increasingly higher temperatures. An antisense Lehsp100/ClpB cDNA fragment was introduced into the tomato by Agrobacterium-mediated transformation. Antisense lines exhibited an extreme repression of heat-induced expression of Lehsp100/ClpB. The levels of chloroplast HSP60 and small HSP in antisense lines were identical to those of the control plants. After plants preconditioned at 38 degrees C for 2 h were exposed to a lethal heat shock at 46 degrees C for 2 h, the antisense lines were greatly impaired and withered in 21 days of the recovery phase, whereas the untransformed control plants and the vector-transformed plants survived. Furthermore, chlorophyll fluorescence measurements showed that PS II in antisense lines were more susceptible to the thermal irreversible inactivation than the untransformed and vector-transformed control plants. This work provides the first example that induction of chloroplast LeHSP100/ClpB contributes to the acquisition of thermotolerance in higher plants.

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

“…[See online article for color version of this figure.] Katiyar-Agarwal et al, 2003). Cytosolic Hsp70 and plastid ClpB and small heat shock proteins have also been implicated in heat sensitivity of plants (Lee and Schö ffl, 1996;Sung and Guy, 2003;Wang and Luthe, 2003;Miroshnichenko et al, 2005;Myouga et al, 2006;Yang et al, 2006;Lee et al, 2007). However, no such role has been proposed for plastid Hsp70s.…”

Molecular and Genetic Evidence for the Key Role of AtCaM3 in Heat-Shock Signal Transduction in Arabidopsis

“…In plants, heat shock (HS) affects growth and crop production. Most organisms, including higher plants, synthesize heat shock proteins (HSPs) in response to high-temperature stress (Vierling, 1991;Queitsch et al, 2000;Nieto-Sotelo et al, 2002;Charng et al, 2006;Yang et al, 2006). In eukaryotes, expression of HSPs is regulated by heat shock transcription factors (HSFs).…”

Plant Hsp100/ClpB-like proteins: poorly-analyzed cousins of yeast ClpB machine

“…Tomato ClpB/ Hsp100-c was found to be heat shock induced (Yang et al 2006). Gulli et al (2007) reported that four Hsp100 gene transcripts behaved in different manner with respect to each other in response to heat stress in T. durum.…”

“…It was further seen that the overexpression of apg6 inhibited chloroplast development, resulting in a mild pale green phenotype. Yang et al (2006) noted that tomato plants in which expression of chloroplastic ClpB/Hsp100 (ClpB/Hsp100-c) was repressed by an antisense construct, show high temperature sensitivity. Mutant plants in the latter work showed enhanced irreversible thermal inactivation of PSII to high temperature stress.…”