CONICET | Buscador de Institutos y Recursos Humanos

Precise subcellular localization of defense factors is essential for plants immune system. The lipid transfer protein-like AZI1, is an important component for the systemic resistance and priming or immunological ?memory? establishment. Recently, we have demonstrated that AZI1 is needed for the movement of the priming signal azelaic acid (AZA) and a pool of AZI1 exists at the site of AZA production, the plastid envelope. Furthermore, after systemic resistance-triggering infections, the proportion of plastid located AZI1 increases. However, AZI1 does not possess a chloroplastic transit peptide or any other recognizable targeting signal that can explain its localization. Here, we uncover a novel bipartite N-terminal signature that allows AZI1 to target plastids by using a signal anchor-like mechanism. We also show that the key defense-associated kinases MPK3/6 regulate the abundance of AZI1?s plastid pool in leaves and possibly in underground tissues. Interestingly, many Arabidopsis coded proteins display a similar N-terminal signature. Among them we found several NBS-LRR class of resistance (R) proteins, known to be essential plant immune receptors. Microscopy and subcellular fractionation data corroborate the plastid localization for some of them. These are the first R proteins proposed as functioning from plastids, which are crucial organelles for a successful defense response. Consistent with this, preliminary results indicate that KO mutant plants for one of these R proteins are more susceptible to pathogen infections. Taken together, our results indicate the existence of an undescribed mode of plastid targeting probably related to defense responses against pathogens. Particularly with regards to the phenomena of priming, in which a well-placed ambush can be the difference between life and death.