Vitaminsareplantgrowthregulatorsandactivatorsofdefenseresponsesagainstpathogens.The cytomolecular mechanismsinvolvedin the induction ofresistancebychemicalsespeciallyvitaminson monocotyledonous plants are largelyunknown.Here,weshowthatriboflavin,whichactsasadefense activatorinriceagainsteconomicallyimportantsheathblightcausedby Rhizoctoniasolani, primedthe expressionoflipoxygenase(LOX) asakeygeneinoctadecanoidpathway,andenhancedlignification. Exogenousjasmonicacid(JA)applicationonriceinducesresistanceagainst R. solani in amannersimilar to riboflavin.Applicationofjasmonate-deficient rice mutant hebiba and usingaLOXinhibitorrevealed the mainroleofoctadecanoidpathwayinriboflavin-induced resistance (IR).Inriboflavin-treated inoculatedplants,upregulationofphenylalanineammonia-lyase(PAL) expression,asamajormarkerof phenylpropanoidpathway,wasdetecteddownstreamof LOX upregulation. Co-applicationofriboflavin and 5, 8,11,14-eicosatetraynoicacid(ETYA) on rice leavesrevealednoupregulationof PAL and no priminginlignification.Furthermore,lowerlevelsof PAL transcripts andligninweredetectedin hebiba compared with control.Thesefindingsindicatetheroleofoctadecanoidpathwayin the induction of phenylpropanoidmetabolismleadingtolignificationasanovelmechanismofriboflavin-IRin Oryza sativa–R. solani pathosystem.

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