Characterization and biological function of the ISOCHORISMATE SYNTHASE2 gene of Arabidopsis.

Salicylic acid (SA) is an important mediator of plant defense response. In Arabidopsis (Arabidopsis thaliana), this compound was proposed to derive mainly from isochorismate, itself produced from chorismate through the activity of ISOCHORISMATE SYNTHASE1 (ICS1). 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, a second ICS gene of the Arabidopsis genome, in the production of SA. We have shown that ICS2 encodes a functional ICS enzyme and that, similar 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.

Pleiotropic effect of phenolic compounds content increases in transgenic flax plant.

The principal goal of this paper was to generate flax (Linum usitatissimum L.) plants with increased antioxidant properties. To accomplish this a vector containing a multigene construct was prepared, and transgenic plants overexpressing essential flavonoid biosynthesis pathway enzymes were generated and analyzed. The simultaneous expression of genes encoding chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR) resulted in a significant increase of flax antioxidant capacity. To investigate the determinants of higher antioxidant properties of transgenic plants, the phenolic acids and lignans compound contents were measured. In both green part and seed extracts from transgenic plants, the phenolic acids level was increased when compared to the control. The calculated correlation coefficient between phenolic acids content and antioxidant capacity (0.82 and 0.70 for green part and flaxseed, respectively) perfectly reflects their strong relationship. The increase in yield of transgenic plants and their higher resistance to Fusarium culmorum and Fusarium oxysporum when compared to the control plants was a characteristic feature. It was assessed a very high correlation (correlation coefficient = 0.9) between phenolic acids level in flaxseed extract and resistance to F. culmorum. The flowering date of transgenic plants was approximately 3 weeks earlier than that of the control plants. Interestingly, a significant increase in monounsaturated fatty acids and a slight increase in lignans content accompanied the increase in antioxidant properties of flaxseeds.