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Functional characterization of Arabidopsis phototropin 1 in the hypocotyl apex
Author(s) -
Sullivan Stuart,
Takemiya Atsushi,
Kharshiing Eros,
Cloix Catherine,
Shimazaki Kenichiro,
Christie John M.
Publication year - 2016
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.13313
Subject(s) - phototropism , hypocotyl , arabidopsis , phototropin , apex (geometry) , microbiology and biotechnology , petiole (insect anatomy) , biology , cotyledon , botany , gravitropism , mutant , chemistry , biochemistry , blue light , physics , gene , hymenoptera , optics
Summary Phototropin (phot1) is a blue light‐activated plasma membrane‐associated kinase that acts as the principal photoreceptor for shoot phototropism in Arabidopsis in conjunction with the signalling component Non‐Phototropic Hypocotyl 3 ( NPH 3). PHOT 1 is uniformly expressed throughout the Arabidopsis hypocotyl, yet decapitation experiments have localized the site of light perception to the upper hypocotyl. This prompted us to investigate in more detail the functional role of the hypocotyl apex, and the regions surrounding it, in establishing phototropism. We used a non‐invasive approach where PHOT 1– GFP ( P1– GFP ) expression was targeted to the hypocotyl apex of the phot‐deficient mutant using the promoters of CUP ‐ SHAPED COTYLEDON 3 ( CUC 3 ) and AINTEGUMENTA ( ANT ). Expression of CUC 3::P1– GFP was clearly visible at the hypocotyl apex, with weaker expression in the cotyledons, whereas ANT ::P1– GFP was specifically targeted to the developing leaves. Both lines showed impaired curvature to 0.005 μmol m −2 sec −1 unilateral blue light, indicating that regions below the apical meristem are necessary for phototropism. Curvature was however apparent at higher fluence rates. Moreover, CUC 3::P1– GFP partially or fully complemented petiole positioning, leaf flattening and chloroplast accumulation, but not stomatal opening. Yet, tissue analysis of NPH 3 de‐phosphorylation showed that CUC 3::P1– GFP and ANT ::P1– GFP mis‐express very low levels of phot1 that likely account for this responsiveness. Our spatial targeting approach therefore excludes the hypocotyl apex as the site for light perception for phototropism and shows that phot1‐mediated NPH 3 de‐phosphorylation is tissue autonomous and occurs more prominently in the basal hypocotyl.