COI1-Dependent but JA-Ile-Independent Signaling Pathway

COI1 is the receptor for the plant hormone JA-Ile (jasmonoyl-isoleucine). If either COI1 (Xie et al., 1998) or the JA-Ile biosynthesis enzyme allene oxide synthase (AOS; Park et al., 2002) are mutated, plants are more susceptible to necrotrophic pathogens.

In contrast, the aos and the coi1 mutants do not behave in the same manner after infection with Verticillium longisporum. The coi1 mutant is more resistant than the wild-type whereas the aos mutant is as susceptible as the wildtype (Ralhan et al., 2012).

It is concluded that the fungus exploits a JA-Ile-independent COI1 function to trigger susceptibility. Grafting experiments showed that the novel COI1 function is necessary only in the roots. However, it does not interfere with initial colonization of the root and the shoot.

Since wild-type shoots grafted on coi1 roots are resistant, we conclude that a mobile signal is synthesized in roots which alters the physiology of the shoot so that fungal proliferation is supported at later stages of the disease. Synthesis of this signal requires COI1 but not JA-Ile.

• Elucidation of the JA-Ile-independent COI1 function (Interacting proteins?)
• Identification of the mobile signal that renders the shoot more susceptible to the fungus.