A long shot: Photosynthesis-derived systemic signal controls lateral root emergence (Plant Physiol.)

Photosynthesis, in addition to generating ‘food’ for plants, is also known to control root growth, although the mechanism has been unknown. Duan and co-workers identified CYCLOPHILIN38 (CYP38) as necessary for photosynthesis-mediated lateral root (LR) emergence. The chloroplast-localized CYP38 is necessary for assembly of photosystem II, and its mutants show defects in LR emergence, linking it to the elusive shoot-derived signal. Grafting experiments between wild type and cyp38 mutants hinted that CYP38 is required for LR emergence, but the protein itself is not transported from shoot to root. Measurement of endogenous auxin and grafting experiments revealed that roots of cyp38 mutants have reduced auxin levels, but grafting to the wild-type scion led to auxin accumulation in cyp38 root stock. Thus, the authors conclude that photosynthesis regulates LR emergence through systemic shoot-to-root transport of either auxin or a metabolite that induces its biosynthesis. (Summary by Pavithran Narayanan @pavi_narayanan) Plant Physiol. 10.1093/plphys/kiaa032