The CRL plastid outer envelope protein supports TOC75-V / OEP80 complex formation in Arabidopsis

Embedded {beta}-barrel proteins in the outer envelope membrane mediate most cellular traffic between the cytoplasm and the plastids. Although TOC75-V/OEP80 has been implicated in the insertion and assembly of {beta}-barrel proteins in the outer envelope membrane of Arabidopsis thaliana, relatively little is known about this process. CRUMPLED LEAF (CRL) encodes a protein localizing in the outer envelope membrane, and its loss of function 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 with ethyl methanesulfonate revealed that a missense mutation in OEP80 suppresses crls pleiotropic defects. Furthermore, we found that the complex formation of OEP80 was compromised in crl. Furthermore, we demonstrated that CRL interacts with OEP80 in vivo and that a portion of CRL is present in protein complexes with the same molecular weight as the OEP80-associated complex. Our results suggest that CRL interacts with OEP80 to regulate its complex formation. CRL has been shown to be involved in plastid protein import; therefore, pleiotropic defects in crl are likely due to the combined effects of decreased plastid protein import and altered membrane integration of {beta}-barrel proteins in the outer envelope membrane. This study sheds light on the mechanisms that allow the integration of {beta}-barrel proteins into the outer envelope membrane of plastids and the significance of this finding for plant cellular processes.