How do plants coordinate chromatin regulation and hormonal signalling to cope with low temperatures? In a research article published in The Plant Journal, research from the Institut de Biologie Moléculaire des Plantes (IBMP), reveal a previously uncharacterized role for the histone methyltransferase SDG26 in regulating cold stress responses in Arabidopsis thaliana.
Plants constantly face environmental challenges, including sudden drops in temperature. To survive these conditions, they activate complex molecular responses involving changes in gene expression, hormonal signalling and chromatin organization. However, how epigenetic mechanisms contribute to coordinating these responses remains incompletely understood.
In this study, the authors identify SDG26 as an important regulator of plant adaptation to cold. They show that cold exposure increases both SDG26 gene expression and protein abundance. At the molecular level, SDG26 directly associates with several cold-responsive genes, including members of the CBF-COR regulatory pathway, and promotes their expression through the deposition of histone H3 lysine 36 trimethylation (H3K36me3), a chromatin modification associated with active transcription.
Beyond its direct effects on cold-responsive genes, SDG26 also plays a key role in regulating the levels of abscisic acid (ABA), a plant hormone involved in responses to environmental stress. The study shows that SDG26 controls the expression of several genes involved in ABA biosynthesis, degradation and transport. Accordingly, plants lacking SDG26 accumulate less ABA, exhibit impaired cold-induced stomatal closure and display increased sensitivity to drought.
Interestingly, the loss of SDG26 also leads to enhanced freezing tolerance, despite the reduced activation of several cold-responsive genes. This unexpected observation highlights the complexity of plant stress responses and suggests that additional, yet unidentified, mechanisms contribute to freezing adaptation.
Together, these findings reveal SDG26 as an important chromatin-based regulator that integrates ABA-dependent and ABA-independent pathways to coordinate plant responses to environmental stresses. They provide new insights into how epigenetic regulation connects gene expression, hormonal homeostasis and plant adaptation to changing environmental conditions.
