Priming Maritime Pine Megagametophytes during Somatic Embryogenesis Improved Plant Adaptation to Heat Stress

María Amparo Pérez-Oliver,Iva Pavlović,Juan Segura,Ondřej Novák,Isabel Arrillaga,Juan Gregorio Haro,Ester Sales

doi:10.3390/plants10030446

Abstract

In the context of global climate change, forest tree research should be addressed to provide genotypes with increased resilience to high temperature events. These improved plants can be obtained by heat priming during somatic embryogenesis (SE), which would produce an epigenetic-mediated transgenerational memory. Thereby, we applied 37 °C or 50 °C to maritime pine (Pinus pinaster) megagametophytes and the obtained embryogenic masses went through the subsequent SE phases to produce plants that were further subjected to heat stress conditions. A putative transcription factor WRKY11 was upregulated in priming-derived embryonal masses, and also in the regenerated P37 and P50 plants, suggesting its role in establishing an epigenetic memory in this plant species. In vitro-grown P50 plants also showed higher cytokinin content and SOD upregulation, which points to a better responsiveness to heat stress. Heat exposure of two-year-old maritime pine plants induced upregulation of HSP70 in those derived from primed embryogenic masses, that also showed better osmotic adjustment and higher increases in chlorophyll, soluble sugars and starch contents. Moreover, ϕPSII of P50 plants was less affected by heat exposure. Thus, our results suggest that priming at 50 °C at the SE induction phase is a promising strategy to improve heat resilience in maritime pine.

Highlights

Global warming will challenge forest tree populations in boreal and temperate regions in the decades
Our results demonstrated that only the putative WRKY11 gene (WKY) was overexpressed in embryogenic masses (EMs) derived from primed megagametophytes, especially those from the 37 ◦ C treatment (Figure 1) indicating that in maritime pine this gene could be of interest as a priming marker
We can conclude that high-temperature priming during the first steps of somatic embryogenesis (SE) improved adaptation to heat stress in the SE-derived maritime pine plants. These primed plants, especially primed at 50 ◦ C (P50), maintained upregulation of both WRKY11 transcription factor and superoxide dismutase (SOD) genes, that we suggest are responsible of their phenotypes, which are characterized by higher basal levels of hormones (CKs, abscisic acid (ABA), indole acetic acid (IAA)) and by differential responses to heat stress, either short-term pulses or prolonged treatments, as compared to NP plants

Summary

Introduction

Global warming will challenge forest tree populations in boreal and temperate regions in the decades. In the Mediterranean basin, evidence of forest decline during the last decades has already been associated to the combination of high temperatures and droughts, that induce decreased tree growth, massive mortality and die-off events. In this region, mountain forests cope with multiple stresses during summer, such as heat, drought and photoinhibition, and under the on-going climate change scenario, these adverse conditions are expected to become aggravated. Mountain forests cope with multiple stresses during summer, such as heat, drought and photoinhibition, and under the on-going climate change scenario, these adverse conditions are expected to become aggravated This implies that there is an urgent need in developing strategies to increase forest stability against abiotic stresses, proactive adaptive silviculture is recommended for this region [2]. Priming refers to prior exposure to an eliciting factor that makes plants more tolerant to future stress exposure

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