At the node level, what physiological and molecular network regulates branching initiation?

In the literature, many studies have provided a detailed understanding of the hormonal network (auxin, cytokinins, and strigolactones) controlling bud outgrowth, and have highlighted the role of the BRANCHED1 (BRC1) gene as an integrator of the different signals controlling shoot branching (Wang et al., 2019). Our work so far has led to a better understanding of the role of sugar and its interaction with the hormonal network and BRC1. In particular, we have shown that sugar has a signal-promoting role on bud outgrowth and relieves the repressing effect of auxin (Rabot et al., 2012; Barbier et al., 2015; Bertheloot et al., 2020). On the other hand, the combined use of pharmacological experiments and quantitative modeling has shown that the antagonistic action of sugar to auxin results, at least in part, from a repression of the strigolactone pathway, through which auxin acts on the bud (Bertheloot et al., 2020; Figure 1). Finally, the combination of pharmacological, metabolomic, and transcriptomic approaches supports the critical role of the primary sugar metabolism (glycolysis-The TCA cycle/The-Oxidative Pentose Phosphate Pathway) of the bud in the integration of sugar and auxin signals. More interestingly, primary sugar metabolism acts upstream of the integrator gene BRC1, regulating its abundance through two different pathways involving two distinct regions of BRC1 promoter (Wang etal., 2021, Figure 2).

Our future work aims to further understand the mechanisms involved in the response of buds to sugar and different hormones (in particular cytokinins) and to determine the importance of sugar metabolism in the response of buds to environmental signals. We are also interested in the role of small non-coding RNAs, which are highlighted to play a major role in the regulation of plant development. The main objective will be to better our understanding on the complexity of the mechanisms governing the ability of the bud to grow out and to identify the major regulatory networks.