Shoko Ueki, Ph.D. Research Assistant Professor Department of Biochemistry and Cell Biology Life Science Building, Rm. 438A Stony Brook University Stony Brook, NY 11794-5215 Office telephone: 631-632-1004 Fax: 631-632-8575 E-mail: sueki@ms.cc.sunysb.edu
Research Description

cdiGRP/GrIP/GLA system on regulation of PD. Callose level at PD is determined by activities of callose synthase (CalS, (i)) and GLA (ii). PD is a transport pathway for various types of macromolecules, such as nucleic acids and protein (iii). We have previously demonstrated that cdiGRP and GrIP induces callose accumulation at PD. In addition, we have identified GLA as cdiGRP interactor by two hybrid screening. Furthermore, GLA alone is capable of increasing PD permeability possibly by digesting callose at PD. These observations suggest us that cdiGRP (and possibly GrIP) binds to GLA to inhibit its enzymatic activity and/or blocks its access to substrate callose, resulting in increasing callose level at PD (v). We propose that cdiGRP, GrIP and GLA serve as important components of the regulatory machinery to control macromolecular cell-to-cell transport via PD (vi). (Note that ER spanning through PD is not illustrated in this figure intentionally.)

Intercellular communications, both between adjacent and distant cells, are vital for multicellular organisms to orchestrate whole-body physiology. Plants have evolved a unique pathway for such intercellular communication, termed symplastic transport. Symplastic transport allows for the direct exchange of macromolecules among neighboring cells through channel structures, plasmodesma (PD), and rapid, long distance transport via phloem. This mode of molecular trafficking is quite important for signal transduction in plants, enabling the regulation of many biological events in the tissues. For example, the PD is implicated in local and systemic transduction of RNA silencing signals, an important plant defense system. Moreover, selective trafficking of some transcription factors to adjacent cells has been implicated in tissue differentiation in the apical meristem and root. Plant viruses pirate this transport pathway to establish systemic host infection. Although the importance of PD as a passageway for macromolecules is well established, its molecular structure and regulatory machinery remain largely unknown. We utilized plant viruses as probes for analyzing regulatory mechanism of this symplastic pathway, and characterized functions of three proteins, cadmium induced glycine rich protein (cdiGRP), cdiGRP-interacting protein (GrIP), and putative 1,3-b-D-glucanase (GLA), that are involved in regulation of transport through PD. The 1,3-b-D-glucan (termed callose) is one of few factors known to regulate PD: it serves as ‘molecular sphincter’, and accumulation of callose at PD restricts macromolecular trafficking through the channel. We have discovered that cdiGRP and GrIP are positive regulators for callose levels. Moreover, We have discovered that GLA, an enzyme that degrade callose and increases PD permeability, also binds to cdiGRP in vitro.

Based on these discoveries, we posit that GrIP, cdiGRP, and GLA form a system that is playing crucial role in regulation of PD permeability (see Figure below). We will continue to explore the implications of these proteins in PD regulatory mechanisms for the next few years. We will pursue three specific research goals: (1) Characterization of the functional link between the cdiGRP, GrIP, and GLA, (2) Characterization of PD-regulation by cdiGRP, GrIP, and GLA, and (3) Understanding the role of cdiGRP/GrIP/GLA in whole-plant physiology.

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