Branch angle responses to photosynthesis are partially dependent on TILLER ANGLE CONTROL 1

Light serves as an important environmental cue in regulating plant architecture. Previous work had demonstrated that both photoreceptor-mediated signaling and photosynthesis play a role in determining the orientation of plant organs. TILLER ANGLE CONTROL 1 (TAC1) was recently shown to function in setting the orientation of lateral branches in diverse plant species, but the degree to which it plays a role in light-mediated phenotypes is unknown. Here, we demonstrated that TAC1 expression was light dependent, as expression was lost under dark or far-red growth conditions, but did not display any clear diurnal rhythm. Loss of TAC1 in the dark was gradual, and experiments with photoreceptor mutants indicated this was not dependent upon Red/Far-Red or Blue light signaling, but partially required the signaling integrator CONSTITUTIVE PHOTOMORPHGENESIS 1 (COP1). Over-expression of TAC1 partially prevented the narrowing of branch angles in the dark or under Far-Red light. Treatment with the carotenoid biosynthesis inhibitor Norflurazon or the PSII inhibitor DCMU led to loss of TAC1 expression similar to dark or far-red conditions, but surprisingly expression increased in response to the PSI inhibitor Paraquat. Our results indicate that TAC1 plays an important role in modulating plant architecture in response to photosynthetic signals.\n\nHIGHLIGHTBranch angles narrow in darkness or under far-red light. This response is partially mediated by TAC1 which responds to photosynthetic signals, providing a key link between photosynthesis and plant architecture.