Pine Trees and Temperature: How Cold and Heat Shape Their Future

It is well-known that plants can be influenced by their surroundings. For maritime pines, temperature changes during early growth can lead to significant differences in how they develop. This was discovered through experiments that altered the temperature during the maturation of pine embryos. The results showed that pines grown in colder or warmer conditions than usual developed distinct traits. These traits included variations in leaf structure, proline content, photosynthesis efficiency, and hormone levels. Moreover, these pines responded differently to short-term heat stress. To understand the reasons behind these changes, scientists examined the genes expressed in the embryonic tissue of these pines. They found that 812 genes were expressed differently in the altered temperature conditions. In the cold-grown pines, ten genes related to epigenetic regulation were more active. Some of these genes are known to play a role in the maturation of somatic embryos. Notably, three genes—histone deacetylases HDA9, a histone-lysine methyl-transferase, and an Argonaute—showed increased activity due to the cold temperature. This suggests that low temperatures can leave epigenetic marks on these genes. In the warm-grown pines, genes related to stress response were more active. These included genes involved in the abscisic acid-mediated response, such as those encoding Ras GTPase-activating protein-binding proteins, an AAA-ATPase, and an aspartyl protease. Additionally, genes related to the production of jasmonic acid, cytokinins, and the diterpene pimaradiene were also more active. However, the increased levels of ABA and cytokinins in the warm-grown pines could not be fully explained by the gene activity in their embryonic tissue. In contrast, the cold-grown pines showed reduced activity in genes encoding an ABA receptor and a xyloglucan endotrans-glucosylase/hydrolase. This supports the idea that the heat-adapted traits observed in the cold-grown pines—such as faster proline increase, lower ABA levels, stable cytokinins, and better photosynthesis recovery—are due to epigenetic changes induced by the cold temperature. These changes were not present in the warm-grown pines. This research highlights the complex ways in which temperature can shape the genetic and physiological traits of maritime pines. It also raises questions about how these findings can be applied to tree breeding programs and our understanding of plant adaptation to environmental stresses.