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.

Agrarian and Environmental Sciences Department Institute of Environmental Sciences University of Zaragoza High Polytechnic School Ctra Cuarte s n 22071 Huesca Spain

Laboratory for Chemical Biology Division of MoLecular Biology Ruđer Bošković Institute Bijenička cesta 54 10000 Zagreb Croatia

Laboratory of Growth Regulators Faculty of Science Institute of Experimental Botany of the Czech Academy of Sciences Palacký University Šlechtitelů 27 783 71 Olomouc Czech Republic

Plant Biology Department Faculty of Pharmacy Biotechnology and Biomedicine Institute Universidad de Valencia Vicent Andrés Estellés s n Burjassot 46100 Valencia Spain

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Changing Temperature Conditions during Somatic Embryo Maturation Result in Pinus pinaster Plants with Altered Response to Heat Stress