Physiological and Molecular Assessment of Altered Expression of Hsc70-1 in Arabidopsis. Evidence for Pleiotropic Consequences

Abstract

Hsp70s function as molecular chaperones. The protective chaperone activities of hsp70 help to confer tolerance to heat, glucose deprivation, and drought. Overexpression of hsp70s in many organisms correlates with enhanced thermotolerance, altered growth, and development. To better understand the roles of hsp70 proteins in Arabidopsis, the molecular and physiological consequences of altered expression of the major heat shock cognate, Hsc70-1, were analyzed. Extensive efforts to achieve underexpression of Hsc70-1 mRNA using a full-length antisense cDNA resulted in no viable transgenic plants, suggesting that reduced expression is lethal. Constitutive overexpression of Hsc70-1 also appeared to be deleterious to viability, growth, and development because fewer transformants were recovered, and most were dwarfed with altered root systems. Despite being dwarfed, the overexpression plants progressed normally through four selected developmental stages. Heat treatment revealed that Hsc70-1 overexpression plants were more tolerant to heat shock (44°C for 10 min). The elevated basal levels of HSC70-1 in transgenic plants led to delayed heat shock response of several heat shock genes. The data in this study suggest that tight regulation of Hsc70-1 expression is critical for the viability of Arabidopsis and that the functions of HSC70-1 contribute to optimum growth, development, thermotolerance, and regulation of the heat shock response.

Dual function of an Arabidopsis transcription factor DREB2A in water-stress-responsive and heat-stress-responsive gene expression

“…AtHsfA3 is a member of the HSF gene family, which consists of 21 genes belonging to three major classes that are based on structural differences, HsfA, HsfB, and HsfC. HsfAs, have been shown to be the major transcription factors that function in heat-induced expression of HSP genes (24). AtHsfA3 might act as a transcription factor in HS-stress-responsive gene expression, but detailed function of AtHsfA3 has not yet been identified.…”

“…The expression of some HSP genes is reported to be induced not only by HS but also by drought stress (22). HSPs act as molecular chaperones by maintaining homeostasis of protein folding and thus help to maintain the metabolic and structural integrity of cells (22)(23)(24). HSP expression is regulated at the transcriptional level by HS transcription factors (HSFs), which recognize the conserved HS element in the promoter regions of HSP genes (24)(25)(26).…”

“…HSPs act as molecular chaperones by maintaining homeostasis of protein folding and thus help to maintain the metabolic and structural integrity of cells (22)(23)(24). HSP expression is regulated at the transcriptional level by HS transcription factors (HSFs), which recognize the conserved HS element in the promoter regions of HSP genes (24)(25)(26). Arabidopsis contains 21 different HSF genes (27), and this high multiplicity suggests the importance of backup and diversification of HSFs.…”

Heat Shock Protein Cognate 70-4 and an E3 Ubiquitin Ligase, CHIP, Mediate Plastid-Destined Precursor Degradation through the Ubiquitin-26S Proteasome System inArabidopsis

“…In addition, the four other cytosolic Hsc70 isoforms exhibited increased transcript levels, albeit to a lesser extent ( Figure 2B). Previous studies have shown that Hsc70-1 mediates heat tolerance, plant development, immune response, abiotic stress response, and protein targeting to the nuclear envelope membrane (Sung and Guy, 2003;Noë l et al, 2007;Brkljacic et al, 2009;Cazalé et al, 2009). Thus, each cytosolic Hsc70 isoform may have a specific function, with a degree of functional redundancy among the isoforms (Noë l et al, 2007).…”

Functional analysis of Hsp70 superfamily proteins of rice (Oryza sativa)

“…Whereas DnaK system efficiently solubilized and refolded small protein aggregates (Diamant et al 2000), large protein aggregates are solubilized in concert with Hsp100/ ClpB (Diamant et al 2000;Acebron et al 2009). Expression of cytosolic Hsp70 genes is linked to acquired thermotolerance because of their property to reactivate the protein aggregates formed under various stress conditions (Lee and Schoffl 1996;Yang et al 2009;Qi et al 2011;Zhou et al 2012;Sung and Guy 2003). It is noted that Hsp70 may function as a negative feedback regulator of HSF activity (Shi et al 1998;Kim and Schoffl 2002).…”