Molecular characterization of His-Asp phosphorelay signaling factors in maize leaves: implications of the signal divergence by cytokinin-inducible response regulators in the cytosol and the nuclei.
Genes for histidyl-aspartyl (His-Asp) phosphorelay components (His-containing phosphotransfer proteins, HP, and response regulators, RR) were isolated from Zea mays L. to characterize their function in cytokinin signaling. Six type-A RRs (ZmRR1, ZmRR2, ZmRR4-ZmRR7), 3 type-B RRs (ZmRR8-ZmRR10), and 3 HPs (ZmHP1-ZmHP3) were found in leaves. All type-A RR genes expressed in leaves were up-regulated by exogenous cytokinin. Transient expression of fusion products of the signaling modules with green fluorescent protein in epidermal leaf cells suggested cytosolic and nuclear localizations of ZmHPs, whereas type-B ZmRR8 was restricted to the nucleus. Type-A RRs were localized partly to the cytosol (ZmRR1, ZmRR2, and ZmRR3) and partly to the nucleus (ZmRR4, ZmRR5, and ZmRR6). In the yeast two-hybrid assay, ZmHP1 and ZmHP3 interacted with both cytosolic ZmRR1 and nuclear type-B ZmRRs. In vitro experiments demonstrated that ZmHPs function as a phospho-donor for ZmRRs; turnover rates of the phosphorylated state were tenfold lower in ZmRR8 and ZmRR9 than in ZmRR1 and ZmRR4. These results suggest that the His-Asp phosphorelay signaling pathway might diverge into a cytosolic and a nuclear branch in leaves of maize, and that the biochemical nature of ZmRRs is different in terms of stability of the phosphorylated status.
Asakura
Yasuharu
Y
Plant Science Center, RIKEN (Institute of Physical and Chemical Research), 1-7-22, Suehiro, Tsurumi, Yokohama 230-0045, Japan.
Hagino
Takeshi
T
Ohta
Yukinori
Y
Aoki
Koh
K
Yonekura-Sakakibara
Keiko
K
Deji
Atsushi
A
Yamaya
Tomoyuki
T
Sugiyama
Tatsuo
T
Sakakibara
Hitoshi
H
D001224:Aspartic Acid / Q000378:metabolism*; D002467:Cell Nucleus / Q000235:genetics; D003001:Cloning, Molecular; D003583:Cytokinins / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D014644:Genetic Variation; D049452:Green Fluorescent Proteins; D006639:Histidine / Q000378:metabolism*; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D018749:RNA, Plant / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D017422:Sequence Analysis, DNA; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics*; D020798:Two-Hybrid System Techniques; D003313:Zea mays / Q000235:genetics*
D003583:Cytokinins; D018076:DNA, Complementary; D008164:Luminescent Proteins; D010940:Plant Proteins; D018749:RNA, Plant; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D001224:Aspartic Acid; D006639:Histidine