Matsubayashi Yoshikatsu, Shinohara Hidefumi, Ogawa Mari
Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8601, Japan.
Chem Rec. 2006;6(6):356-64. doi: 10.1002/tcr.20090.
Almost all plant cells, even when fully differentiated, can dedifferentiate and proliferate in vitro to form a callus, in which they can then differentiate to form various organs. These sequential processes can be promoted by exposing the cells to a conditioned medium in which either the same or other cells have previously been grown, indicating the involvement of cell-to-cell communication mediated by a chemical factor. This factor was purified from the conditioned medium and identified as a 5-amino-acid sulfated peptide. The addition of this peptide, named phytosulfokine (PSK), to the culture medium, even at nanomolar concentrations, significantly promotes cellular proliferation and/or cellular differentiation. We purified a membrane receptor for PSK (PSKR1) by ligand-based affinity chromatography and identified it as a member of leucine-rich repeat receptor kinases. The PSK-binding domain of PSKR1 was further identified by ligand photoaffinity labeling using a novel "on-column photoaffinity labeling" methodology that allows repeated incorporation of the photoaffinity label. Analysis of loss-of-function and gain-of-function mutants of the Arabidopsis PSKR1 revealed that PSK signaling affects cellular longevity and potential for growth without interfering with basic plant morphogenesis. These results suggest that PSK represents a new class of hormones that affect the potential for cellular growth and longevity of individual cells via binding to PSKR1, thereby exerting a pleiotropic effect on individual cells in response to environmental conditions.
几乎所有植物细胞，即使在完全分化后，也能在体外脱分化并增殖形成愈伤组织，然后在愈伤组织中再分化形成各种器官。将细胞暴露于先前已培养过相同或其他细胞的条件培养基中，可促进这些连续过程，这表明存在由化学因子介导的细胞间通讯。该因子从条件培养基中纯化出来，被鉴定为一种含5个氨基酸的硫酸化肽。将这种名为植物硫肽激素（PSK）的肽添加到培养基中，即使浓度为纳摩尔级，也能显著促进细胞增殖和/或细胞分化。我们通过基于配体的亲和层析纯化了PSK的膜受体（PSKR1），并将其鉴定为富含亮氨酸重复序列受体激酶家族的成员。使用一种新型的“柱上光亲和标记”方法，通过配体光亲和标记进一步鉴定了PSKR1的PSK结合结构域，该方法允许重复掺入光亲和标记。对拟南芥PSKR1功能缺失和功能获得突变体的分析表明，PSK信号传导影响细胞寿命和生长潜力，而不干扰植物的基本形态发生。这些结果表明，PSK代表了一类新的激素，它通过与PSKR1结合来影响单个细胞的生长潜力和寿命，从而在响应环境条件时对单个细胞产生多效性作用。
