The miR319-targeted TCP transcription factors play crucial roles in the establishment of Arabidopsis thaliana shoot architecture in response to carbon and nitrogen availability.

Shoot branching is a highly plastic developmental process that allows plants to adjust their architecture to environmental conditions, such as carbon and nitrogen availability. Although the class II TCP transcription factor BRANCHED1 is a well-established repressor of shoot branching, the contribution of other TCP factors during this process remains less well understood. Here, we show that the miR319-targeted TCP module promotes shoot branching in Arabidopsis thaliana. Overexpression of miR319 reduced rosette branch production, whereas repression of TCP3 activity or triple knockout (KO) mutation in TCP3, TCP4 and TCP10 inhibited branching. Conversely, expression of a miR319-resistant TCP3 triggered a highly branched phenotype, indicating that TCP3 and related miR319 targets act as positive regulators of shoot branching. Genetic analysis with the strigolactone-deficient max4 mutant showed that strigolactones mediate, at least partly, the reduced branching observed in the miR319 overexpressing line and in the tcp3,4,10 triple mutant. Transcriptomic and DNA-binding analyses indicated indirect effect of TCP3 on strigolactone biosynthesis genes. Instead, miR319 overexpression increased the sensitivity of branching to nitrogen limitation and reduced nitrate uptake, thereby increasing the expression of strigolactone synthesis genes. We further show that carbon starvation reduced the transcription levels of miR319-targeted TCPs, independently of miR319 accumulation, and that TCP3 may connect carbon availability to sugar signalling via HEXOKINASE1. Together, our results identify the miR319-targeted TCP module as a positive regulator of shoot branching that links plant architecture to carbon and nitrogen availability.