期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：11
DOI：10.1073/pnas.2123353119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Although plastid division is critical for plant development, how components of the plastid division machinery (PDM) are imported into plastids remains unexplored. A forward genetic screen to identify suppressors of a
crumpled leaf (
crl) mutant deficient in plastid division led us to find dominant gain-of-function (GF) mutations in
TIC236, which significantly increases the import of PDM components and completely rescues
crl phenotypes. The defective plastid division phenotypes in
crl and
tic236-knockdown mutants and CRL-TIC236 association in a functional complex indicate that the CRL-TIC236 module is vital for plastid division. Hence, we report the first GF translocon mutants and unveil CRL as a novel functional partner of TIC236 for PDM import.
TIC236 is an essential component of the translocon for protein import into chloroplasts, as evidenced by the embryonic lethality of the knockout mutant. Here, we unveil a TIC236-allied component, the chloroplast outer membrane protein CRUMPLED LEAF (CRL), absence of which impairs plastid division and induces autoimmune responses in
Arabidopsis thaliana. A forward genetic screen exploring CRL function found multiple dominant
TIC236 gain-of-function (
tic236-gf) mutations that abolished
crl-induced phenotypes. Moreover, CRL associates with TIC236, and a
tic236-knockdown mutant exhibited multiple lesions similar to the
crl mutant, supporting their shared functionality. Consistent with the defective plastid division phenotype of
crl, CRL interacts with the transit peptides of proteins essential in plastid division, with
tic236-gf mutations reinforcing their import via increased TIC236 stability. Ensuing reverse genetic analyses further revealed genetic interaction between CRL and SP1, a RING-type ubiquitin E3 ligase, as well as with the plastid protease FTSH11, which function in TOC and TIC protein turnover, respectively. Loss of either SP1 or FTSH11 rescued
crl mutant phenotypes to varying degrees due to increased translocon levels. Collectively, our data shed light on the links between plastid protein import, plastid division, and plant stress responses.
