Tissue-type specific accumulation of the plastoglobular proteome, transcriptional networks and plastoglobular functions.

Plastoglobules (PGs) are dynamic protein-lipid micro-compartments in plastids enriched for isoprenoid-derived metabolites. Chloroplast PGs support formation, remodeling and controlled dismantling of thylakoids during developmental transitions and environmental responses. However, the specific molecular functions of most PG proteins are still poorly understood. This review harnesses recent co-mRNA expression data from combined microarray and RNAseq information in ATTED-II on an updated inventory of 34 PG proteins, as well as proteomics data across 30 Arabidopsis tissue types from ATHENA. Hierarchical clustering based on relative abundance for the PG proteins across non-photosynthetic and photosynthetic tissue types showed their coordinated protein accumulation across Arabidopsis parts, tissue types, development and senescence. Evaluation of mRNA-based forced networks at different coefficient thresholds identified a central hub with seven PG proteins and four peripheral modules. Enrichment of specific nuclear transcription factors (e.g. Golden2-like) and support for cross-talk between PGs and the plastid gene expression was observed, and specific ABC1 kinases appear part of a light signaling network. Examples of other specific findings are that FBN7b is involved with upstream steps of tetrapyrrole biosynthesis and that ABC1K9 is involved in starch metabolism. This review provides new insights in PG protein functions and an improved framework for experimental studies.