Reversible phosphorylation of NPH3/RPT2-like proteins regulates phototropin receptor signaling.
Sullivan S, Hermanowicz P, Higa T, Waksman T, Gotoh E
Summary
6.8/10Plants have light-sensing proteins that help them bend toward light and move their chloroplasts. Two enzymes (PP2C phosphatases) control how long this response stays active by removing chemical marks. When these enzymes fail, plants can't bend toward light properly, suggesting they're critical for seedlings to break through soil.
Key Findings
PP2C19 and PP2C35 phosphatases regulate NPH3 dephosphorylation at S744, controlling phototropism; pp2c mutants show sustained phosphorylation and reduced light-bending response
Clade L PP2Cs control both auxin-dependent (phototropism) and auxin-independent (chloroplast movement) light responses, with greater defects in double mutants indicating functional redundancy
PP2C19 defects impair chloroplast light-response movement in both Arabidopsis and Marchantia, demonstrating conserved function across plant species
Original Abstract
Phototropin receptor kinases (phot1 and phot2) enhance photosynthesis by coordinating light responses such as phototropism and chloroplast repositioning under low blue light conditions. These processes rely on NON-PHOTOTROPIC HYPOCOTYL 3 (NPH3)/ROOT PHOTOTROPISM 2-like (NRL) proteins. The Arabidopsis (Arabidopsis thaliana) NRL protein NPH3 is phosphorylated by phot1 at S744, a modification that alters its localization and promotes hypocotyl phototropism. Although reversible phosphorylation of S744 is necessary for reassembling an active phot1-NPH3 complex at the plasma membrane, the mechanisms driving NPH3 dephosphorylation remain unclear. Here, we show that clade L TYPE 2C PROTEIN PHOSPHATASES (PP2C19 and PP2C35) regulate S744 phosphorylation and NPH3 function. Mutants lacking PP2C19 exhibit sustained S744 phosphorylation and reduced phototropism, with greater defects observed in pp2c19 pp2c35 double mutants, indicating functional redundancy between these phosphatases. Moreover, clade L pp2c mutants display altered RPT2 phosphorylation and abundance and modulate the phosphorylation status of NRL PROTEIN FOR CHLOROPLAST MOVEMENT 1 (NCH1), suggesting broader regulatory control over phot1-NRL targets. Consistent with this, phototropin-dependent chloroplast accumulation is impaired in both Arabidopsis and Marchantia pp2c19 mutants. These findings identify clade L PP2Cs as key regulators of auxin-dependent (phototropism) and auxin-independent (chloroplast accumulation movement) light responses which, together with their additional role in regulating hypocotyl gravitropism, are particularly important for seedling emergence and establishment from beneath the soil surface.
Species Mentioned
Arabidopsis (rockcress) is a genus of small flowering plants in the cabbage and mustard family, Brassicaceae. Arabidopsis species are native to temperate and subarctic Eurasia and North America, North Africa, and the mountains of eastern tropical Africa. This genus is of great interest since it c...
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