Plantation Forestry under Global Warming: Hybrid Poplars with Improved Thermotolerance Provide New Insights on the in Vivo Function of Small Heat Shock Protein Chaperones    

Abstract

Climate-driven heat stress is a key factor affecting forest plantation yields. While its effects are expected to worsen during this century, breeding more tolerant genotypes has proven elusive. We report here a substantial and durable increase in the thermotolerance of hybrid poplar (Populus tremula 3 Populus alba) through overexpression of a major small heat shock protein (sHSP) with convenient features. Experimental evidence was obtained linking protective effects in the transgenic events with the unique chaperone activity of sHSPs. In addition, significant positive correlations were observed between phenotype strength and heterologous sHSP accumulation. The remarkable baseline levels of transgene product (up to 1.8% of total leaf protein) have not been reported in analogous studies with herbaceous species. As judged by protein analyses, such an accumulation is not matched either by endogenous sHSPs in both heat-stressed poplar plants and field-grown adult trees. Quantitative real timepolymerase chain reaction analyses supported these observations and allowed us to identify the poplar members most responsive to heat stress. Interestingly, sHSP overaccumulation was not associated with pleiotropic effects that might decrease yields. The poplar lines developed here also outperformed controls under in vitro and ex vitro culture conditions (callus biomass, shoot production, and ex vitro survival), even in the absence of thermal stress. These results reinforce the feasibility of improving valuable genotypes for plantation forestry, a field where in vitro recalcitrance, long breeding cycles, and other practical factors constrain conventional genetic approaches. They also provide new insights into the biological functions of the least understood family of heat shock protein chaperones.

Ectopic expression of a cyanobacterial flavodoxin in creeping bentgrass impacts plant development and confers broad abiotic stress tolerance

“…They bind and stabilize their client proteins that have become denatured under stress conditions. Most of them are highly up‐regulated in response to heat and have a clear role in thermotolerance (Atkinson and Urwin, ; Merino et al ., ; Sun et al ., ; Waters, ). Three AsHSP genes examined in this study, AsHSP17 (Sun et al ., ), AsHSP26.7 and AsHSP26.8 (Wang and Luthe, ), were all significantly induced, but differentially regulated in WT and the TG plants (Figure ), suggesting Fld implication in triggering one of the important stress response mechanisms, contributing to an enhanced plant tolerance to heat.…”

Constitutive Expression of a Tomato Small Heat Shock Protein Gene LeHSP21 Improves Tolerance to High-Temperature Stress by Enhancing Antioxidation Capacity in Tobacco

“…Gene expression of some sHSPs has been detected in all plant tissues under different conditions (Almoguera et al 1993;Coca et al 1996;Sun et al 2001;Verdaguer et al 2003;Swindell 2006;Swindell et al 2007;Qin et al 2008;Siddique et al 2008;Waters et al 2008;Sarkar et al 2009;Weston et al 2011;Haq et al 2013;Merino et al 2014;Park et al 2015). In rice, the Oshsp26 gene was induced by heat stress: the transcript level was the highest when rice leaves were treated at 42°C for 2 h. It was also found that Oshsp26 gene was expressed following oxidative stress even in the absence of heat stress (Lee et al 2000).…”

“…In tobacco, constitutive expression of the tomato mitochondrial small heat shock protein enhanced thermotolerance in transgenic plants (Sanmiya et al 2004). A substantial and durable increase in the thermotolerance through overexpression of a major small heat shock protein (sHSP) was also achieved in hybrid poplar (Populus tremula × Populus alba) (Merino et al 2014).…”

Transgenic creeping bentgrass overexpressing Osa‐miR393a exhibits altered plant development and improved multiple stress tolerance

“…Heat tolerance is associated with induced expression of heat-shock proteins in plants (Queitsch et al, 2000;Sun et al, 2002;Zhong et al, 2013). Overexpression of HSP leads to enhanced heat tolerance has also been observed in various plant species (Kim et al, 2012;Merino and G omez, 2014;Mu et al, 2013;Murakami et al, 2004;Sato and Yokoya, 2008;Sun et al, 2012). In creeping bentgrass, chloroplast-localized small heat-shock proteins (CP-sHSPs) play an important role in heat tolerance (Wang and Luthe, 2003).…”