The FIBRILLIN multigene family in tomato, their roles in plastoglobuli structure and metabolism

Plastoglobuli (PG) are plant lipoprotein compartments, present in plastid organelles. They are involved in the formation and/or storage of lipophilic metabolites. FIBRILLINs (FBN) are one of the main PG-associated proteins and are particularly abundant in carotenoid-enriched chromoplasts found in ripe fruits and flowers. To address the contribution of different FBNs to isoprenoid sequestration and PG function, a multiplex gene editing approach was undertaken. Analysis of single and high-order fbn mutants for the major PG-related FBNs in tomato, namely SlFBN 1, SlFBN 2a, SlFBN 4, SlFBN 7a, revealed functional redundancy. High order fbn mutants displayed phenotypes associated with abnormal isoprenoid accumulation, and aberrant PG formation and morphology. Lipidomic analysis highlighted broader changes in lipid metabolism. Paralog-specific roles were also observed and included the regulation of specific isoprenoids (e.g., plastochromanol) and control of plastidial esterification capability by SlFBN7a. Collectively, the results support both structural and regulatory roles of SlFBNs in PGs. Our findings expose fundamental aspects of metabolic compartmentalisation in plant cells and the importance of lipoprotein particles for their plastid metabolism/physiology. Significance statement In the chromoplast of ripe tomato fruit and flower, plastoglobuli (PGs) are associated with several important biotechnological traits, due to their functional involvement in metabolism, developmental transitions, and environmental adaption. FIBRILLINS (FBN) are a multigene family of proteins that are collectively major components of the PG. Using a multiplex CRISPR-Cas9 approach single and high-order fbn mutants have been developed. Functional redundancy amongst the members of the FBN multigene family was evident, but also paralog specific functions/influence. Aberrant plastoglobuli formation and altered lipid metabolism are evident among fbn mutants. Characterisation of this resource has shed light on the functional role of FBN and their role in PG formation. This strategy offers new potential for the development of nutritional enhanced and climate resilient crops. ### Competing Interest Statement The authors have declared no competing interest.