Figure 1.

Scopoletin biosynthesis is induced in Arabidopsis during post‐invasion non‐host defence of Pp.

(a) Micrographs of representative interaction sites of Pp with Arabidopsis wild‐type (wt), pen2, and pen2 pad4 sag101 plants at 2 days after inoculation with uredospores. Leaves were subjected to trypan blue staining and inspected by bright‐field microscopy. sp, uredospore; gt, germ tube; ap, appressorium; pc, penetrated cell; hy, intercellular growing hypha; hmc. haustorial mother cell; ha, haustorium.

(b) Schematic depiction of representative Pp interactions with different Arabidopsis genotypes. Black, fungal structures; grey, dying plant epidermal cell.

(c) Microarray analysis revealed significantly (P < 0.05) increased (red box) mRNA abundance of PPP genes for scopoletin biosynthesis, yet unaltered (white box) or repressed (blue box) expression of flavonoid biosynthesis genes in the Arabidopsis pen2 mutant 2 days after inoculation with Pp relative to mock‐treated (0.01% (v/v) Tween‐20) controls. These changes in PPP gene activity are absent in the wild‐type or the pen2 pad4 sag101 triple mutant. Expression values are derived from three independent experiments, each comprising pools of four plants per treatment and genotype.

F6′H1 mRNA (d) and scopoletin accumulation (e) were confirmed by RT‐qPCR and high‐performance liquid chromatography analysis, respectively, in three additional experiments. F6′H1 transcript abundance was normalized to ACT2 as the reference gene. In each experiment, RNA and scopoletin were extracted from 5 g of pooled leaves (~12 plants) per genotype and treatment. Shown are the average values and standard deviation of three independent experiments. Asterisks indicate significant differences to the adequate mock control (Holm–Sidak's multiple comparisons test; P < 0.01).