Poster: Intercellular Signaling

Abs # 804: Phytosulfokine, a key factor regulating cellular dedifferentiation in plants

Presenter:	Matsubayashi, Yoshikatsu , matsu@agr.nagoya-u.ac.jp
Authors	Matsubayashi, Yoshikatsu  (A)   Kihara, Hitomi  (A)   Ogawa, Mari  (A)   Niwa, Masaaki  (A)   Sakagami, Youji  (A)
Affiliations:	(A): Graduate School of Bio-Agricultural Sciences, Nagoya University

Apart from animal cells, plant cells, even at a fully differentiated stage, can dedifferentiate and proliferate in vitro as a totipotent stem cells called callus by the treatment with plant hormones. Relative rate of cellular dedifferentiation, however, strictly depends on the cell density, even if sufficient amounts of auxin/cytokinin are supplied, indicating that additional intercellular signal(s) play a role in this step. One such factor is the 5-amino-acid peptide phytosulfokine (PSK). Together with auxin/cytokinin, PSK induces plant cells to dedifferentiate and re-enter the cell cycle at nanomolar concentrations. PSK also stimulates redifferentiation such as tracheary element differentiation of Zinnia mesophyll cells and somatic embryogenesis in carrot. These cellular dedifferentiation and redifferentiation, however, can not be induced by PSK alone but require certain ratios and concentrations of auxin/cytokinin in addition to PSK. One possibility is that PSK confers a certain type of competence on individual cells and auxin/cytokinin consecutively determine cell fate in plants. Five paralogous genes encoding PSK precursors have been identified in Arabidopsis. PSK mRNAs are found not only in callus cells but also detected in leaves and roots of intact plant, indicating that PSK expression is not limited to the region in which individual cells actively divide. PSK receptor is an LRR receptor kinase with 21 LRRs and a 36-amino acid island domain. Interestingly, transgenic callus overexpressing PSK receptor showed accelerated proliferation, but were unable to regenerate roots and shoots. In this presentation, we will discuss the fundamental function of PSK signaling in plants from the genetic and biochemical point of view.