JA-Ile signalling in Solanum nigrum is not required for defence responses in nature.

Jasmonate signalling plays a central role in activating the plethora of responses that are elicited by herbivory. Solanum nigrum plants silenced in the expression of genes involved in jasmonic acid biosynthesis (irlox3), conjugation (irjar4) and perception (ircoi1) were used to study the function of these genes in the field and in the regulation of transcriptional and metabolic responses. In the field, damage from Noctuidea larvae was four- to fivefold higher on irlox3 and ircoi1 than on wild-type (WT) plants, whereas damage to irjar4 plants was similar to WT levels. Damage rates reflected plant survival rates; fewer irlox3 (78%) and ircoi1 (22%) plants survived compared with irjar4 and WT plants of which all plants survived. Gene expression profiling in leaves 3 h after simulated herbivory revealed differential regulation of ∼700 genes in irlox3 and ircoi1 plants but of only six genes in irjar4 compared with WT plants. Surprisingly, transcriptional responses were not reflected in metabolomic responses; 48 h after simulated herbivory, irjar4 plants showed a 50% overlap in their metabolic profile with ircoi1 plants. Together, these results reveal that SnJAR4 does not play a direct role in herbivore defence, but suggests that SnJAR4 is involved in responses other than those to herbivory.