Involvement of DNA methylation in the control of cell growth during heat stress

Under adverse environmental conditions plants are able to significantly modify their growth pattern to give priority to the activation of defense responses. The redistribution of cell cycle activity and the control of cell expansion are key events in the acclimation of plants to stress. In this work we show that exposure of tobacco BY-2 cells to heat stress caused a significant reduction in growth: firstly a decrease in cell division and successively an inhibition of cell expansion occurred. The inhibition of mitosis seems to be due to the arrest of cell cycle progression at the G2-M checkpoint. Indeed, a decrease in cyclin A, cyclin B and CDKB expression and an increase in Cyclin D3 expression were observed. At the same time the inhibition of cell expansion was accompanied by an under-expression of expansin-8, a protein involved in the regulation of cell wall flexibility. Interestingly, changes observed in the methylative state of the promoters of Cyclin D3 and expansin-8 were well correlated with the alteration in their expression, suggesting that an epigenetic control of these genes could be involved in the inhibition of growth observed under heat stress