The cell wall protein fraction (CWP) is purified from the non-pathogenic biocontrol agent Pythium oligandrum and is composed of two glycoproteins (POD-1 and POD-2), which are structurally similar to class III elicitins. In tomato plants treated with CWP, jasmonic acid (JA)- and ethylene (ET)-dependent signaling pathways are activated, and resistance to Ralstonia solanaceraum is enhanced. To dissect CWP-induced defense mechanisms, we investigated defense gene expression and resistance to bacterial pathogens in Arabidopsis thaliana ecotype Col-0 treated with CWP. When the leaves of Col-0 were infiltrated with CWP, neither visible necrosis nor salicylic acid (SA)-responsive gene (PR-1 and PR-5) expression was induced. In contrast, JA-responsive gene (PDF1.2 and JR2) expression was up-regulated and the resistance to R. solanaceraum and Pseudomonas syringae pv. tomato DC3000 was enhanced in response to CWP. Such CWP-induced defense responses were completely compromised in CWP-treated coi1-1 and jar1-1 mutants with an impaired JA signaling pathway. The induction of defense-related gene expression after CWP treatment was partially compromised in ET-insensitive ein2-1 mutants, but not in SA signaling mutants or nahG transgenic plants. Global gene expression analysis using cDNA array also suggested that several other JA- and ET-responsive genes, but not SA-responsive genes, were up-regulated in response to CWP. Further analysis of CWP-induced defense responses using another eight mutants with impaired defense signaling pathways indicated that, interestingly, the induction of JA-responsive gene expression and enhanced resistance to two bacterial pathogens in response to CWP were completely compromised in rar1-1, rar1-21, sgt1a-1, sgt1b (edm1) and npr1-1 mutants. Thus, the CWP-induced defense system appears to be regulated by JA-mediated and SGT1-, RAR1- and NPR1-dependent signaling pathways.

Enhancing nitrogen utilization is important in maintaining crop yield under low nitrogen conditions. Therefore, rice plants (Oryza sativa L.) were transformed with pMLH7133-RNRT2, which bears OsNRT2.1, a major gene involved in nitrate uptake under low nitrate concentrations. Two transgenic plants harboring an OsNRT2.1 transgene were identified and used for further study. In transgenic plants, OsNRT2.1 was expressed constitutively in roots, while in wild-type plants, the transcript was detected 30 min after starting to supply nitrate. No co-suppression between transgene and host gene was observed, as was observed on introduction of a nitrate reductase gene from the same species. One of the transformants grew faster than the wildtype cultivars when KNO 3 or NH 4 NO 3 was supplied as a nitrogen source. However, no increase in nitrate uptake by young plants was observed. These results suggest that constitutive expression of OsNRT2.1 might enhance vegetative growth and that introduction of genes involved in nitrate uptake from the same species may be useful for genetic improvement of plant growth under low nitrogen conditions. Further studies are necessary to understand the molecular and physiological bases of expression of NRT2.1 in relation to plant growth.