Arabidopsis fibrillin 1-2 subfamily exerts their functions via specific protein-protein interactions

Fibrillins (FBNs) are plastidial proteins found in photosynthetic organisms, from cyanobacteria to higher plants. However, the function of most FBNs remains unknown. We focused on FBN members of the subgroup comprising FBN1a, FBN1b, and FBN2. We show that these three polypeptides interact between each other, potentially forming a network around the plastoglobule surface. Both FBN2 and FBN1s interact with allene oxide synthase (AOS), and the elimination of any of these FBNs results in a delay in jasmonate-mediated anthocyanin accumulation in response to a combination of moderate high light and low temperature. Mutations in FBN1s or FBN2 also affect the protection of PSII under the combination of these stresses. Fully developed leaves of these mutants have lower maximum quantum efficiency of PSII (Fv/Fm) and higher oxidative stress than WT. These effects are additive and the fbn1a-1b-2 triple mutant shows a more severe decrease in Fv/Fm and a higher increase in oxidative stress than fbn1a-1b or fbn2 mutants. Co-immunoprecipitation analysis indicated that FBN2 also interacts with other proteins involved in different metabolic processes. We propose that these fibrillins exert their functions facilitating accurate positioning of different proteins involved in distinct metabolic processes, and that their elimination lead to dysfunction of those proteins.