Fig. 7: Model for miR156-enabled phenotypic plasticity to temperature and light changes.

Environmental light and temperature changes perceived by the photoreceptor and thermosensor PHYB trigger profound modulations in plant architecture via the master growth regulators PIFs and PIF-induced auxin synthesis and signaling. This study unveils a previously unknown control of auxin sensitivity licensed by miR156. Auxin sensitivity is antagonized primarily by SPL9. In light- and temperature-elicited hypocotyl elongation responses during Arabidopsis seedling establishment, miR156 enables auxin sensitivity by repressing SPL9. We propose that miR156-dependent auxin sensitivity constitutes a genetic circuit gating light and temperature responses by the endogenous developmental program. This critical role of miR156 makes the basic components involved in miRNA biogenesis and function, such as DCL1, HYL1, SE, and AGO1, necessary elements for the plant’s phenotypic plasticity in response to environmental temperature and light changes.