Plant hormone signalling through the eye of the mass spectrometer.

Plant growth and development are regulated by hormones and the associated signalling pathways share several common steps, the first being the detection of the signal by receptor proteins. This typically leads to conformational changes in the receptor, thereby modifying its spectrum of interaction partners. Next, secondary signals are transmitted via rapid post-translational cascades, such as targeted phosphorylation or ubiquitination, resulting in the activation/deactivation, relocalization or degradation of target proteins. These events finally give rise to the signal-dependent read-out, such as changes in gene expression and regulation of protein activity. So far, the majority of studies aimed at unravelling hormone signalling pathways in plants relied on genetic or transcriptomic approaches. During the last decade however, MS-driven proteomic methods became increasingly popular tools in plant research as they reveal the specific mechanisms controlled by phytohormones, which for a large part occur on the level of the proteome. Here, we provide an up-to-date review on the growing body of work in these areas using MS-based techniques, with a focus on nonpeptide plant hormones.