Characterization and biological function of the ISOCHORISMATE SYNTHASE 2 gene of Arabidopsis thaliana

Salicylic acid (SA) is an important mediator of plant defense response. In Arabidopsis thaliana, this compound was proposed to derive mainly from isochorismate, itself produced from chorismate through the activity of ICS1 (Isochorismate Synthase1). Null ics1 mutants still accumulate some SA, suggesting the existence of an enzymatic activity redundant with ICS1 or of an alternative ICS-independent SA biosynthetic route. Here we studied the role of ICS2, second ICS gene of the Arabidopsis genome, in the production of SA. We have shown that ICS2 encodes a functional ICS enzyme and that, similarly to ICS1, ICS2 is targeted to the plastids. Comparison of SA accumulation in the ics1, ics2 and ics1 ics2 mutants indicates that ICS2 participates in the synthesis of SA but in limited amounts, that become clearly detectable only when ICS1 is lacking. This unequal redundancy relationship was also observed for phylloquinone, another isochorismate-derived end-product. Furthermore, detection of SA in the double ics1 ics2 double mutant that is completely devoid of phylloquinone provides genetic evidence of the existence of an ICS-independent SA biosynthetic pathway in Arabidopsis

Immune interferon induced by phytohemagglutinin in nude mouse spleen cells.

Phytohemagglutinin is able to trigger interferon synthesis in spleen cell cultures from nude (nu/nu) mice as effectively as in splenic cell cultures from haired, control (nu/+), thymus-bearing mice. A minor theta-bearing cell population present in the spleen of nude mice appears essential to phytohemagglutinin interferon production, although cooperating cells are also required. The properties of nude mouse phytohemagglutinin interferon are indistinguishable from those displayed by the interferon induced in thymus-bearing mouse spleen cell cultures. Both interferons are unstable at pH 2 and cannot be neutralized by an antiviral interferon serum; hence, their characteristics correspond to those described for type T interferon. As in the case of viral interferon, pretreatment of L cells with nude phytohemagglutinin interferon induced specific enhanced phosphorylation of a 67,000-molecular-weight protein in vitro when cell extracts were incubated with double-stranded RNA and gamma-[32P]ATP

Modifying enzyme activity in plants

The present invention is directed to targeting genes and genomes, modifying the activity of enzymes and protein expression in plants. In particular, the present invention relates to methods for reducing the activity of one or more endogenous glycosyltransferases such as N-acetylglucosaminyltransferase, f(1,2)-xylosyltransferase and a(1,3)-fucosyl- transferase in a plant cell and to plants obtained by said method