Abstract
Chloroplast ATP synthase (cpATPase) is an importance thylakoid membrane-associated photosynthetic complex involved in the light-dependent reactions of photosynthesis. In this study, we isolated and characterized a rice (Oryza sativa) mutant yellow leaf 1 (yl1), which exhibits chlorotic leaves throughout developmental stages. The YL1 mutation showed reduced chlorophyll contents, abnormal chloroplast morphology, and decreased photochemical efficiency. Moreover, YL1 deficiency disrupts the expression of genes associated with chloroplast development and photosynthesis. Molecular and genetic analyses revealed that YL1 is a nucleus-encoded protein with a predicted transmembrane domain in its carboxyl-terminus that is conserved in the higher plant kingdom. YL1 localizes to chloroplasts and is preferentially expressed in green tissues containing chloroplasts. Immunoblot analyses showed that inactivation of YL1 leads to drastically reduced accumulation of AtpA (α) and AtpB (β), two core subunits of CF1αβ subcomplex of cpATPase, meanwhile, a severe decrease (ca. 41.7%) in cpATPase activity was observed in the yl1-1 mutant compared with the wild type. Furthermore, yeast two-hybrid and bimolecular fluorescence complementation assays revealed a specific interaction between YL1 and AtpB subunit of cpATPase. Taken together, our results suggest that YL1 is a plant lineage-specific auxiliary factor involved in the biogenesis of the cpATPase complex, possibly via interacting with the β-subunit.
Highlights
Bacterial F0F1-ATP synthases, active plant cpATPase complexes comprise a rotary motor composed of two subcomplexes, the partially membrane-intrinsic, hydrophobic subcomplex CF0 and the membrane-extrinsic, soluble subcomplex CF1
Compared to the number of auxiliary proteins found to function in the assembly of mitochondrial ATP synthase in yeast, surprisingly few auxiliary proteins involved in cpATPase assembly have been characterized to date[13]
We report the identification of rice protein YL1, a nucleus-encoded chloroplast protein, which appears to be involved in the biogenesis of the chloroplast ATPase complex, possibly through interaction with the AtpB subunit
Summary
Bacterial F0F1-ATP synthases, active plant cpATPase complexes comprise a rotary motor composed of two subcomplexes, the partially membrane-intrinsic, hydrophobic subcomplex CF0 and the membrane-extrinsic, soluble subcomplex CF1. Several auxiliary proteins that support the biogenesis of mitochondrial ATP synthase have been identified in Saccharomyces cerevisiae by screening for respiration-defective yeast mutants[15,16,17,18,19] Many of these proteins do not have obvious homologs in chloroplasts[14], and it is likely that plant-specific assembly factors are required for the biosynthesis and assembly of cpATPase[20]. In Arabidopsis, AtPAB directly interacts with the nucleus-encoded γsubunit and functions downstream of chaperonin 60 (Cpn60)-mediated CF1γsubunit folding to promote its assembly into the active CF1 core[23] The characterization of these auxiliary factors has opened up the possibility of gaining insights into the mechanism underlying the biogenesis of this complex. We show that YL1 physically interacts with AtpB, a plastid-encoded βsubunit of cpATPase, indicating its possible role in efficient biogenesis of the cpATPase in plant chloroplasts
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