A major challenge of the coming years is to reduce environmental impacts of agriculture while maintaining, if not increasing, crop yields. One solution to reduce fertilizer inputs is to increase the efficiency of crops using them, for example by increasing root growth and resistance to abiotic stresses. Phytostimulants are molecular effectors that when used in small quantities boost plant growth, in particular the root system. Knowing how phytostimulants work in plants could greatly help to use them more rationally, and assess their safety to environment. In any case, this knowledge is frequently asked to obtain marketing authorisation, as for any new agrochemical. The private partner has identified biosourced phytostimulants improving resistance to abiotic stress, root growth, N, S and P contents and increase yields in crops such as rapeseed, pea, soybean and maize. Interestingly, some of these phytostimulants also improve the Arabidopsis root growth in phosphate deficiency condition. The aim of this project is to: 1) Understand how the biosourced phytostimulants improve crop rooting and yields, in particular under abiotic stress; 2) Use these biosourced phytostimulants as new tools to study a multi-stress signalling pathway of Arabidopsis; Through 6 tasks, a private company and two academic partners will collaborate in physiology, genetics, molecular biology, biochemistry, biophysics and metabolomic experiments in order to reach these three aims.