Thioglucoside glucohydrolase (myrosinase), TGG1, is a strikingly abundant protein in Arabidopsis guard cells. We investigated responses of tgg1-3, tgg2-1 and tgg1-3 tgg2-1 mutants to abscisic acid (ABA) and methyl jasmonate (MeJA) to clarify whether two myrosinases, TGG1 and TGG2, function during stomatal closure. ABA, MeJA and H(2)O(2) induced stomatal closure in wild type, tgg1-3 and tgg2-1, but failed to induce stomatal closure in tgg1-3 tgg2-1. All mutants and wild type showed Ca(2+)-induced stomatal closure and ABA-induced reactive oxygen species (ROS)production. A model is discussed in which two myrosinases redundantly function downstream of ROS production and upstream of cytosolic Ca(2+) elevation in ABA and MeJA signaling in guard cells.

The dynamics of polyphosphate with respect to toal phosphorus and orthophosphate levels in an arbuscular mycorrhizal association were investigated to clarify the role of polyphosphate in the symbiotic phospharus-translocation.Lotus japonicus was inoculated with Glomus sp. HR1 and grown in a two- compartment culture system in which hyphal and mycorrhizal compartments were separated by nylon mesh bags. Extraradical hyphae and mycorrhizal roots were collected from the hyphal and mycorrhizal compartments, respectively, at one h interval after phosphate application to the hyphal compartment, and polyphosphate, total phosphorus and orthophosphate levels were determined. Total phosphorus and polyphosphate levels in hyphae in the hyphal compartment increased and decreased synchronously after phosphate application, while orthophosphate levels remained constant at lower levels. The level of polyphosphate reached 64% of total phosphorus 5 h after phosphate application. Decreases in polyphosphate in hyphae in the hyphal compartment were concurrent with increases in polyphosphate in the mycorrhizal roots + hyphae in the mycorrhizal compartment. The present study demonstrated that the potential capacity of arbuscular mycorrhizal fungal cell for polyphosphate accumulation was much larger than those reported previously and suggested that polyphosphate plays a central role in the mediation of long-distance phosphorus-translocation through hyphae

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Proliferating cell nuclear antigen (PCNA) is post-translationally modified in yeast and animal cells. Major studies carried out in the last decade have focused on the role of sumoylated and ubiquitinated PCNA. Using different approaches, an interaction between plant PCNA and SUMO both in vivo and in bacteria has been demonstrated for the first time. In addition, identical sumoylation patterns for both AtPCNA1 and 2 were observed in bacteria. The plant PCNA sumoylation pattern has been shown to differ significantly from that of Saccharomyces cerevisiae. This result contrasts with a common opinion based on previous structural analysis of yeast, human, and plant PCNAs, which treats PCNA as a highly conserved protein even between species. Analyses of AtPCNA post-translational modifications using different SUMO proteins (SUMO1, 2, 3, and 5) revealed similar modification patterns for each tested SUMO protein. Potential target lysine residues that might be sumoylated in vivo were identified on the basis of in bacteria AtPCNA mutational analyses. Taken together, these results clearly show that plant PCNA is post-translationally modified in bacteria and may be sumoylated in a plant cell at various sites. These data open up important new perspectives for further detailed studies on the role of PCNA sumoylation in plant cells.