Subcellular targeting of an evolutionarily conserved plant defensin M t D ef4.2 determines the outcome of plant–pathogen interaction in transgenic A rabidopsis

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Summary: The M edicago truncatula gene encoding an evolutionarily conserved antifungal defensin M t D ef4.2 was cloned and characterized. I n silico expression analysis indicated that M t D ef4.2 is expressed in many tissues during the normal growth and development of M . truncatula . M t D ef4.2 exhibits potent broad‐spectrum antifungal activity against various F usarium spp . Transgenic A rabidopsis thaliana lines in which M t D ef4.2 was targeted to three different subcellular compartments were generated. These lines were tested for resistance to the obligate biotrophic oomycete H yaloperonospora arabidopsidis N oco2 and the hemibiotrophic fungal pathogen F usarium graminearum PH ‐1. M t D ef4.2 directed to the extracellular space, but not to the vacuole or retained in the endoplasmic reticulum, conferred robust resistance to H . arabidopsidis . Siliques of transgenic A rabidopsis lines expressing either extracellularly or intracellularly targeted M t D ef4.2 displayed low levels of resistance to F . graminearum , but accumulated substantially reduced levels of the mycotoxin deoxynivalenol. The data presented here suggest that extracellularly targeted M t D ef4.2 is sufficient to provide strong resistance to the biotrophic oomycete, consistent with the extracellular lifestyle of this pathogen. However, the co‐expression of extracellular and intracellular M t D ef4.2 is probably required to achieve strong resistance to the hemibiotrophic pathogen F . graminearum which grows extracellularly and intracellularly.

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