The Plant Cell http://doi.org/bs67 (2016)

Light is vital for plants to create sugars through photosynthesis. However, too much light can lead to photodamage. So, plants produce anthocyanins to protect themselves. As with many other danger signals, mitogen-activated protein kinases (MAPKs) are activated by excess light. Jin-Long Qiu and colleagues from Beijing and Copenhagen connect the two processes in Arabidopsis.

The authors used a constitutively activated form of MPK4 in a yeast assay to identify the transcription factor MYB75 as a MAPK substrate. MYB75 controls anthocyanin biosynthesis, is degraded in the dark through the constitutive photomorphogenic 1 (COP1) pathway, and both mpk4 and myb75 mutants failed to accumulate anthocyanin under high light. Multiple lines of evidence show that MPK4 is activated by light and phosphorylates MYB75, which can then escape proteasomal degradation and induce pigment synthesis.

This study shows that MYB75 is a post-transcriptional point of convergence between two opposite pathways; it is degraded by COP1 in the dark, and stabilized by MPK4 in the light. Given the wide occurrences of MAPK activation and anthocyanin synthesis in response to stress, it is significant to discover a molecular link between both pathways.