CRUMPLED LEAF supports plastid OUTER ENVELOPE PROTEIN OF 80 KDA complex formation in Arabidopsis.

Embedded ß-barrel proteins in the outer envelope membrane mediate most cellular trafficking between the cytoplasm and plastids. Although the TRANSLOCON AT THE OUTER ENVELOPE MEMBRANE OF CHLOROPLASTS 75-V (TOC75-V)/OUTER ENVELOPE PROTEIN OF 80 KDA (OEP80) complex has been implicated in the insertion and assembly of ß-barrel proteins in the outer envelope membrane of Arabidopsis (Arabidopsis thaliana) chloroplasts, relatively little is known about this process. CRUMPLED LEAF (CRL) encodes a chloroplast outer envelope membrane-localized protein, and its loss-of-function mutation results in pleiotropic defects, including altered plant morphogenesis, growth retardation, suppression of plastid division, and spontaneous light intensity-dependent localized cell death. A suppressor screen conducted on mutagenized crl mutants revealed that a missense mutation in OEP80 suppresses the pleiotropic defects of crl. Furthermore, we found that OEP80 complex formation is compromised in crl. Additionally, we demonstrated that CRL interacts with OEP80 in vivo and that a portion of CRL is present at the same molecular weight as the OEP80 complex. Our results suggest that CRL interacts with OEP80 to facilitate its complex formation. CRL is involved in plastid protein import; therefore, the pleiotropic defects in crl are likely due to the combined effects of decreased plastid protein import and altered membrane integration of ß-barrel proteins in the outer envelope membrane. This study sheds light on the mechanisms that allow ß-barrel protein integration into the plastid outer envelope membrane and the importance of this finding for plant cellular processes.

Polycomb-dependent differential chromatin compartmentalization determines gene coregulation in Arabidopsis.

In animals, distant H3K27me3-marked Polycomb targets can establish physical interactions forming repressive chromatin hubs. In plants, growing evidence suggests that H3K27me3 acts directly or indirectly to regulate chromatin interactions, although how this histone modification modulates 3D chromatin architecture remains elusive. To decipher the impact of the dynamic deposition of H3K27me3 on the Arabidopsis thaliana nuclear interactome, we combined genetics, transcriptomics, and several 3D epigenomic approaches. By analyzing mutants defective for histone H3K27 methylation or demethylation, we uncovered the crucial role of this chromatin mark in short- and previously unnoticed long-range chromatin loop formation. We found that a reduction in H3K27me3 levels led to a decrease in the interactions within Polycomb-associated repressive domains. Regions with lower H3K27me3 levels in the H3K27 methyltransferase clf mutant established new interactions with regions marked with H3K9ac, a histone modification associated with active transcription, indicating that a reduction in H3K27me3 levels induces a global reconfiguration of chromatin architecture. Altogether, our results reveal that the 3D genome organization is tightly linked to reversible histone modifications that govern chromatin interactions. Consequently, nuclear organization dynamics shapes the transcriptional reprogramming during plant development and places H3K27me3 as a key feature in the coregulation of distant genes.