title: Regulation of root greening by light and auxin/cytokinin signaling in Arabidopsis.
abstract: Tight coordination between plastid differentiation and plant development is best evidenced by the synchronized development of photosynthetic tissues and the biogenesis of chloroplasts. Here, we show that Arabidopsis thaliana roots demonstrate accelerated chlorophyll accumulation and chloroplast development when they are detached from shoots. However, this phenomenon is repressed by auxin treatment. Mutant analyses suggest that auxin transported from the shoot represses root greening via the function of indole-3-acetic acid14, auxin response factor7 (ARF7), and ARF19. Cytokinin signaling, on the contrary, is required for chlorophyll biosynthesis in roots. The regulation by auxin/cytokinin is dependent on the transcription factor long hypocotyl5 (HY5), which is required for the expression of key chlorophyll biosynthesis genes in roots. The expression of yet another root greening transcription factor, golden2-like2 (GLK2), was found to be regulated in opposing directions by auxin and cytokinin. Furthermore, both the hormone signaling and the GLK transcription factors modified the accumulation of HY5 in roots. Overexpression of GLKs in the hy5 mutant provided evidence that GLKs require HY5 to maximize their activities in root greening. We conclude that the combination of HY5 and GLKs, functioning downstream of light and auxin/cytokinin signaling pathways, is responsible for coordinated expression of the key genes in chloroplast biogenesis.
authors.affiliation: Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan. kkobayashi@bio.c.u-tokyo.ac.jp
authors.forename: Koichi
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Baba
authors.forename: Takeshi
authors.initials: T
authors.lastname: Obayashi
authors.forename: Mayuko
authors.initials: M
authors.lastname: Sato
authors.forename: Kiminori
authors.initials: K
authors.lastname: Toyooka
authors.forename: Mika
authors.initials: M
authors.lastname: Keränen
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Fukaki
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohta
authors.forename: Keiko
authors.initials: K
authors.lastname: Sugimoto
authors.forename: Tatsuru
authors.initials: T
authors.lastname: Masuda
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism; D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism; D002734:Chlorophyll / Q000096:biosynthesis*; D002736:Chloroplasts / Q000378:metabolism / Q000648:ultrastructure; D003583:Cytokinins / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D008027:Light; D009687:Nuclear Proteins / Q000378:metabolism; D010937:Plant Growth Regulators / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism / Q000528:radiation effects*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: C503426:ARF19 protein, Arabidopsis; C503425:ARF7 protein, Arabidopsis; D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D003583:Cytokinins; C468868:GLK2 protein, Arabidopsis; C109254:HY5 protein, Arabidopsis; C507566:IAA14 protein, Arabidopsis; D007210:Indoleacetic Acids; D009687:Nuclear Proteins; D010937:Plant Growth Regulators; D014157:Transcription Factors; D002734:Chlorophyll