Co-overexpression of two Heat Shock Factors results in enhanced seed longevity and in synergistic effects on seedling tolerance to severe dehydration and oxidative stress

José-María Personat,Pilar Prieto-Dapena,Javier Tejedor-Cano,Concepción Almoguera,Juan Jordano

doi:10.1186/1471-2229-14-56

José-María Personat, Pilar Prieto-Dapena + Show 3 more

Open Access

https://doi.org/10.1186/1471-2229-14-56

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Abstract

BackgroundWe have previously reported that the seed-specific overexpression of sunflower (Helianthus annuus L.) Heat Shock Factor A9 (HaHSFA9) enhanced seed longevity in transgenic tobacco (Nicotiana tabacum L.). In addition, the overexpression of HaHSFA9 in vegetative organs conferred tolerance to drastic levels of dehydration and oxidative stress.ResultsHere we found that the combined overexpression of sunflower Heat Shock Factor A4a (HaHSFA4a) and HaHSFA9 enhanced all the previously reported phenotypes described for the overexpression of HaHSFA9 alone. The improved phenotypes occurred in coincidence with only subtle changes in the accumulation of small Heat Shock Proteins (sHSP) that are encoded by genes activated by HaHSFA9. The single overexpression of HaHSFA4a in vegetative organs (which lack endogenous HSFA9 proteins) did not induce sHSP accumulation under control growth conditions; neither it conferred thermotolerance. The overexpression of HaHSFA4a alone also failed to induce tolerance to severe abiotic stress. Thus, a synergistic functional effect of both factors was evident in seedlings.ConclusionsOur study revealed that HaHSFA4a requires HaHSFA9 for in planta function. Our results strongly support the involvement of HaHSFA4a and HaHSFA9 in transcriptional co-activation of a genetic program of longevity and desiccation tolerance in sunflower seeds. These results would also have potential application for improving seed longevity and tolerance to severe stress in vegetative organs.

Highlights

We have previously reported that the seed-specific overexpression of sunflower (Helianthus annuus L.) Heat Shock Factor A9 (HaHSFA9) enhanced seed longevity in transgenic tobacco (Nicotiana tabacum L.)
We have shown that the ectopic overexpression of HaHSFA9 from Cauliflower mosaic virus (CaMV) 35S sequences in tobacco seedlings conferred dramatic resistance of green organs and of whole seedlings to severe dehydration [12]
We have proposed that HaHSFA4a and HaHSFA9 might synergistically coactivate the same genetic program of seed longevity and desiccation tolerance in sunflower [15]

Summary

Introduction

We have previously reported that the seed-specific overexpression of sunflower (Helianthus annuus L.) Heat Shock Factor A9 (HaHSFA9) enhanced seed longevity in transgenic tobacco (Nicotiana tabacum L.). The overexpression of HaHSFA9 in vegetative organs conferred tolerance to drastic levels of dehydration and oxidative stress. In the plant zygotic embryo, during orthodox seed maturation, different gene expression programs activate mechanisms that prevent and repair severe desiccation damage, at the same time allowing prolonged survival of the dry mature seed (reviewed [1,2,3,4] and references therein). Whole 35S:A9 seedlings resisted drastic oxidative stress conditions, as treatments in the dark with 200 mM H2O2 for 24 h [13]. The photosynthetic apparatus of the 35S:A9 seedlings, as well as other cellular membranes, resisted such stress conditions [13]. In all these instances, HaHSFA9 overexpression activated genes that encode sHSPs from different classes. Most of the HaHSFA9-induced sHSPs are expressed mainly (or exclusively) during zygotic embryogenesis in seeds

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