Mitogen-activated protein kinases (MAPK) play key roles in plant immunity
against pathogens. However, it is still unclear if SlMKKs genes, which are
MAPKs from tomato, also have an effect on a plant's resistance against the
fungal pathogen Botrytis cinerea commonly known as gray mold.

Five SlMKK genes were identified in tomato and analyzed. It revealed that
the expression of two of the five SlMKK genes, SlMKK2 and SlMKK4, was
induced by gray mold. This showed that SlMKK2 and SlMKK4 were the only ones
involved with the resistance to gray mold. Silencing either of the two
resulted in reduced resistance to gray mold in tomato plants.

Silencing of SlMKK2 and SlMKK4 expression in tomato demonstrate that both of
these genes function as positive regulators of defense response against gray
mold.

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