Fibrillin 2 interacts with other proteins to protect photosystem II against abiotic stress in Arabidopsis

Fibrillins (FBNs) are plastidial proteins found in photosynthetic organisms, from cyanobacteria to higher plants. The function of most FBNs is largely unknown. We focused on the subgroup formed by FBN1a, -1b, and -;2, which has been proposed to be involved in the photoprotection of photosystem II (PSII), though their mechanism of action has not yet been characterized. We show that FBN2 interacts with FBN1a and with other FBN2 polypeptides, potentially forming a network around the plastoglobule surface. Both FBN2 and FBN1 interact with the allene oxide synthase, 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. FBN2 also interacts with other proteins involved in different metabolic processes. Mutants lacking FBN2 demonstrate less photoprotection of PSII, alterations that are not found in fbn1a-fbn1b mutants. We also show that FBN2 interacts with Acclimation of Photosynthesis to Environment 1 (APE1), and gene co-expression analysis suggests that both proteins are involved in the same metabolic process. The elimination of APE1 leads to lesions in PSII under abiotic stress similar to observations in fbn2 mutants, with lower maximum and effective quantum yield. However, a reduction in non-photochemical quenching is observed exclusively in fbn2 mutants, suggesting that other FBN2-interacting proteins are responsible for this alteration. We propose that FBN2 facilitates accurate positioning of different proteins involved in distinct metabolic processes, and its elimination leads to dysfunction in those proteins. One sentence summaryFibrillin 2 protects photosynthesis against abiotic stresses by facilitating the accurate positioning of different proteins involved in distinct processes, and its elimination leads to dysfunction in those proteins