Spatial gene expression analysis in tomato hypocotyls suggests cysteine as key precursor of vascular sulfur accumulation implicated in Verticillium dahliae defense

Verticillium dahliae is a prominent generator of plant vascular wilting disease and sulfur (S)‐enhanced defense ( SED ) mechanisms contribute to its in‐planta elimination. The accumulation of S‐containing defense compounds ( SDCs ) including elemental S ( S 0 ) has been described based on the comparison of two near‐isogenic tomato ( Solanum lycopersicum ) lines differing in fungal susceptibility. To better understand the effect of S nutrition on V. dahliae resistance both lines were supplied with low, optimal or supraoptimal sulfate‐S. An absolute quantification demonstrated a most effective fungal elimination due to luxury plant S nutrition. High‐pressure liquid chromatography ( HPLC ) showed a strong regulation of Cys levels and an S‐responsive GSH pool rise in the bulk hypocotyl. High‐frequency S peak accumulations were detected in vascular bundles of resistant tomato plants after fungal colonization by laser ablation‐inductively coupled plasma‐mass spectrometry ( LA‐ICP‐MS ). Global transcriptomic analysis suggested that early steps of the primary S metabolism did not promote the SDCs synthesis in the whole hypocotyl as gene expression was downregulated after infection. Enhanced S fertilization mostly alleviated the repressive fungal effect but did not reverse it. Upregulation of glutathione ( GSH )‐associated genes in bulk hypocotyls but not in vascular bundles indicated a global antioxidative role of GSH . To finally assign the contribution of S metabolism‐associated genes to high S 0 accumulations exclusively found in the resistant tomato line, a spatial gene expression approach was applied. Laser microdissection of infected vascular bundles revealed a switch toward transcription of genes connected with cysteine (Cys) synthesis. The upregulation of LeOASTLp1 suggests a role for Cys as key precursor for local S accumulations (possibly S 0 ) in the vascular bundles of the V. dahliae ‐resistant tomato line.