FtsHi1/ARC1 is an essential gene in Arabidopsis that links chloroplast biogenesis and division

Abstract

SUMMARYThe Arabidopsis arc1 (accumulation and replication of chloroplasts 1) mutant has pale seedlings and smaller, more numerous chloroplasts than the wild type. Previous work has suggested that arc1 affects the timing of chloroplast division but does not function directly in the division process. We isolated ARC1 by map-based cloning and discovered it encodes FtsHi1 (At4g23940), one of several FtsHi proteins in Arabidopsis. These poorly studied proteins resemble FtsH metalloproteases important for organelle biogenesis and protein quality control but are presumed to be proteolytically inactive. FtsHi1 bears a predicted chloroplast transit peptide and localizes to the chloroplast envelope membrane. Phenotypic studies showed that arc1 (hereafter ftsHi1-1), which bears a missense mutation, is a weak allele of FtsHi1 that disrupts thylakoid development and reduces de-etiolation efficiency in seedlings, suggesting that FtsHi1 is important for chloroplast biogenesis. Consistent with this finding, transgenic plants suppressed for accumulation of an FtsHi1 fusion protein were often variegated. A strong T-DNA insertion allele, ftsHi1-2, caused embryo-lethality, indicating that FtsHi1 is an essential gene product. A wild-type FtsHi1 transgene rescued both the chloroplast division and pale phenotypes of ftsHi1-1 and the embryo-lethal phenotype of ftsHi1-2. FtsHi1 overexpression produced a subtle increase in chloroplast size and decrease in chloroplast number in wild-type plants while suppression led to increased numbers of small chloroplasts, providing new evidence that FtsHi1 negatively influences chloroplast division. Taken together, our analyses reveal that FtsHi1 functions in an essential, envelope-associated process that may couple plastid development with division.Keywords: FtsHi, plastid division, embryogenesis, chloroplast biogenesis, plastid development, Arabidopsis thaliana. INTRODUCTIONThe Arabidopsis arc (accumulation and replication of chloroplasts) mutants exhibit various defects in chloroplast size and number in leaf mesophyll cells and define a suite of 12 nuclear genes, ARC1-ARC12, that influence chloroplast division and expansion (Pyke and Leech, 1992, 1994;Marrison et al., 1999;Pyke, 1999). Most of the arc mutants have fewer and larger chloroplasts per cell than the wild type, a hallmark indicator of impaired chloroplast division, and several ARC loci with mutations causing such phenotypes have been shown to encode components of the chloroplast division machinery (Gao et al., 2003;Vitha et al., 2003;Fujiwara et al., 2004;Shimada et al., 2004;Glynn et al., 2007;Yoder et al., 2007). The arc1 mutant is distinct in having smaller and more numerous chloroplasts per cell than the wild type, suggesting that plastid division is accelerated rather than inhibited in this mutant. arc1 seedlings are also pale, indicating a possible role for ARC1 in chloroplast development (Pyke and Leech, 1992, 1994) (Figure 1a). Analysis of double mutants has shown that ARC1 functions in a separate process from other ARC genes (...

Early emergence of the FtsH proteases involved in photosystem II repair

“…Found in the same clade as FtsH12 are the inactive FtsH proteases AtFtsHi1, AtFtsHi2, AtFtsHi4 and AtFtsHi5, which are involved in plastid differentiation during embryogenesis (Kadirjan-Kalbach et al 2012, Lu et al 2014 and, like AtFtsH12, are located in the chloroplast envelope (Ferro et al 2010, Lu et al 2014. Whether AtFtsHi1/2/4/5 subunits are found in the same FtsH complex as AtFtsH12 awaits confirmation.…”

Roles of Arabidopsis PARC6 in Coordination of the Chloroplast Division Complex and Negative Regulation of FtsZ Assembly

“…Constructs were introduced into Agrobacterium tumefaciens GV3101 by electroporation, and plants were transformed by floral dipping (Zhang et al, 2006). T1 transgenic plants were selected on plates containing 20 mg mL 21 hygromycin, then transferred to soil and grown as described (Kadirjan-Kalbach et al, 2012).…”

“…For PARC6::PARC6-Myc complementation lines, leaf tissue was harvested from 4-week-old T1 transgenic plants. Protein samples were prepared as described previously (Kadirjan-Kalbach et al, 2012) with slight modification. Briefly, tissue was ground to powder in liquid nitrogen using an MP FastPrep-24 Tissue and Cell Homogenizer (MP Biomedicals).…”

Amyloplast-Localized SUBSTANDARD STARCH GRAIN4 Protein Influences the Size of Starch Grains in Rice Endosperm

“…Many embryo-defective mutants with the disruption of plastid-targeted proteins have been shown to exhibit the impaired plastid development (Hsu et al, 2010;Bryant et al, 2011). In the case of the Arabidopsis arc1 mutant, the weak allele mutant has smaller, more numerous chloroplasts than the wild type, while the strong transfer DNA insertion allele causes embryo lethality (Kadirjan-Kalbach et al, 2012). ARC1 likely functions in an essential process of plastid development that may be coupled with plastid division.…”