The HaDREB2 transcription factor enhances basal thermotolerance and longevity of seeds through functional interaction with HaHSFA9

Abstract

BackgroundTranscription factor HaDREB2 was identified in sunflower (Helianthus annuus L.) as a drought-responsive element-binding factor 2 (DREB2) with unique properties. HaDREB2 and the sunflower Heat Shock Factor A9 (HaHSFA9) co-activated the Hahsp17.6G1 promoter in sunflower embryos. Both factors could be involved in transcriptional co-activation of additional small heat stress protein (sHSP) promoters, and thus contribute to the HaHSFA9-mediated enhancement of longevity and basal thermotolerance of seeds.ResultsWe found that overexpression of HaDREB2 in seeds did not enhance longevity. This was deduced from assays of basal thermotolerance and controlled seed-deterioration, which were performed with transgenic tobacco. Furthermore, the constitutive overexpression of HaDREB2 did not increase thermotolerance in seedlings or result in the accumulation of HSPs at normal growth temperatures. In contrast, when HaDREB2 and HaHSFA9 were conjointly overexpressed in seeds, we observed positive effects on seed longevity, beyond those observed with overexpression of HaHSFA9 alone. Such additional effects are accompanied by a subtle enhancement of the accumulation of subsets of sHSPs belonging to the CI and CII cytosolic classes.ConclusionOur results reveal the functional interdependency of HaDREB2 and HaHSFA9 in seeds. HaDREB2 differs from other previously characterized DREB2 factors in plants in terms of its unique functional interaction with the seed-specific HaHSFA9 factor. No functional interaction between HaDREB2 and HaHSFA9 was observed when both factors were conjointly overexpressed in vegetative tissues. We therefore suggest that additional, seed-specific factors, or protein modifications, could be required for the functional interaction between HaDREB2 and HaHSFA9.

Inference of Longevity-Related Genes from a Robust Coexpression Network of Seed Maturation Identifies Regulators Linking Seed Storability to Biotic Defense-Related Pathways

“…The longevity module contained a number of genes implicated in previously identified mechanisms conferring longevity, such as DNA repair (DNA LIGASE-1) and protection by the testa pigments (TT7 and mate efflux family protein with high sequence similarity to TT12). Also, the presence of several HSPs (HSP17.6, HSP21, and DnaJ) is in accordance with previous studies demonstrating the importance of these proteins for seed longevity (Almoguera et al, 2009). The identification and further characterization of an a-galactosidase, AGAL2, for which mutant seeds showed decreased longevity and increased sucrose and stachyose contents (Supplemental Figure 6) points to a role of raffinose family oligosaccharide metabolism in longevity.…”

“…Previously, a link between auxin and longevity was established by Carranco et al (2010), who showed an interaction between the auxin/indole-3-acetic acid protein IAA27 and the heat shock factor HSFA9 of Helianthus annuus. HSFA9 activates transcription of specific small heat shock protein (sHSP) genes and is involved in the control of a genetic program that regulates seed longevity (Prieto-Dapena et al, 2006;Almoguera et al, 2009). In our study, ARF binding sites were found in the promoters of the M. truncatula and Arabidopsis HSP21 of the longevity module.…”

HsfA2 Controls the Activity of Developmentally and Stress-Regulated Heat Stress Protection Mechanisms in Tomato Male Reproductive Tissues

“…The implication of Hsf-Hsp networks in developmental programs has been shown for embryogenesis and seed maturation (Almoguera et al, 2009;Kotak et al, 2007;Prieto-Dapena et al, 2008;Wehmeyer and Vierling, 2000). Seed-specific overexpression of the sunflower (Helianthus annuus) HsfA9 in tobacco (Nicotiana tabacum) enhanced the accumulation of Hsps, improved the resistance of seeds against controlled deterioration, and increased seed longevity (Prieto-Dapena et al, 2006).…”

Overexpression of Arabidopsis Dehydration- Responsive Element-Binding Protein 2C Confers Tolerance to Oxidative Stress

“…Recent studies identified heat shock transcription factor A3 (HsfA3) as a highly up-regulated heatinducible gene in transgenic plants over-expressing DREB2s (Chen et al, 2010;Yoshida et al, 2008). Moreover, transient promoter reporter assays using mesophyll protoplasts demonstrated that HsfA3 expression is directly regulated by DREB2s under conditions of heat stress (Chen et al, 2010;Schramm et al, 2008) and that DREB2-overexpressing transgenic plants have increased tolerance to heat stress (Almoguera et al, 2009;Lee et al, 2010;Lim et al, 2007;Matsukura et al, 2010). Recent work established that DREB2C physically interacts with ABF2, a bZIP protein regulating abscisic acid (ABA)-responsive gene expression, and its overexpression affected ABA sensitivity .…”