Capturing hormonal and light interactions in a simulation model of shoot branching

Shoot branching, i.e. axillary bud break and subsequent branch outgrowth, is a key determinant of overall aboveground plant form. During plant development, the number of branches formed strongly influences the amount of light absorbed by the plant, and thus the plant´s competitive strength in terms of light capture in relation to neighbouring plants. Shoot branching is regulated by genetic and physiological factors such as hormones and assimilates. In turn, these internal factors are modulated by environmental signals such as light intensity, light spectral composition and nutrients. The internal and environmental factors are part of a complex feedback system that operates at several levels of biological organization. Here, we present a modelling approach that captures the interactions between hormones and light in the case of shoot branching. We simulated Arabidopsis individually and in a plot at different ratios of ambient red and far-red light (R:FR). A low R:FR resulted in low branching. The individual plants experienced slightly higher R:FR values and produced more branches as a result, depending on ambient R:FR. The model serves a useful scientific tool to integrate knowledge and to improve experimental approaches on shoot branching.