Compounds from rhizosphere microbes that promote plant growth

The rhizosphere is the soil-plant interface colonized by bac-terial and fungal species that exert growth-promoting and adaptive benefits. The plant-bacteria relationships rely upon the perception of volatile organic compounds (VOCs), canon-ical phytohormones such as auxins and cytokinins, and the bacterial quorum sensing-related N-acyl-L-homoserine lac -tones and cyclodipeptides. On the other hand, plant-beneficial Trichoderma fungi emit highly active VOCs, including 6-pentyl-2H-pyran-2-one (6-PP), and b-caryophyllene, which contribute to plant morphogenesis, but also into how these microbes spread over roots or live as endophytes. Here, we describe recent findings concerning how compounds from beneficial bacteria and fungi affect root architecture and advance into the signaling events that mediate microbial recognition.