FIGURE 7.

A model for SA-metabolizing pathways leading to 2,3- and 2,5-DHBA and its various sugar conjugates in Arabidopsis. SA synthesis is promoted during leaf senescence and plant defense, forming a positive feedback loop. This feedback loop is under the positive control of EDS1, FMO1, and PAD2 and under the negative control of both NUDT7 and VTC1. Free cellular SA is removed by SA conjugation with glucose and by SA hydroxylation leading to 2,5-DHBA and subsequent glucose conjugation to 2,5-DHBA glucosides. SA hydroxylation to 2,3-DHBA and subsequent xylose conjugation to 2,3-DHB3X is a newly discovered pathway, representing a detoxification mechanism for SA or 2,3-DHBA or a means of channeling bioactive benzoic acid molecules in cells and tissues (see “Discussion”). The dotted arrows represent uncertainty regarding whether 2,3-DHBA is derived from SA or from isochorismate under normal physiological conditions.