Journal
NEW PHYTOLOGIST
Volume 233, Issue 2, Pages 766-780Publisher
WILEY
DOI: 10.1111/nph.17785
Keywords
cyanobacterium; cytochrome b(559); photosynthesis; photosystem II (PSII); tandem gene amplification
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Funding
- Czech Science Foundation [19-29225X]
- ERC [854126]
- Academia Sinica
- Ministry of Science and Technology in Taiwan [108-2311-B-001-024]
- European Research Council (ERC) [854126] Funding Source: European Research Council (ERC)
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Mutations in the cytochrome (Cyt) b(559) of cyanobacteria lead to PSII deficiency and inability to grow photoautotrophically, but transformants with tandem gene amplification can restore PSII accumulation and achieve photoautotrophic growth.
Cytochrome (Cyt) b(559) is a key component of the photosystem II complex (PSII) that is essential for its proper functioning and assembly. Site-directed mutants of the model cyanobacterium Synechocystis sp. PCC6803 with mutated heme axial ligands of Cyt b(559) have little PSII and are therefore unable to grow photoautotrophically. Here we describe two types of Synechocystis autotrophic transformants that retained the same mutations in Cyt b(559) but are able to accumulate PSII and grow photoautotrophically. Whole-genome sequencing revealed that all of these autotrophic transformants carried a variable number of tandem repeats (from 5 to 15) of chromosomal segments containing the psbEFLJ operon. RNA-seq analysis showed greatly increased transcript levels of the psbEFLJ operon in these autotrophic transformants. Multiple copies of the psbEFLJ operon in these transformants were only maintained during autotrophic growth, while its copy numbers gradually decreased under photoheterotrophic conditions. Two-dimensional PAGE analysis of membrane proteins revealed a strong deficiency in PSII complexes in the Cyt b(559) mutants that was reversed in the autotrophic transformants. These results illustrate how tandem gene amplification restores PSII accumulation and photoautotrophic growth in Cyt b(559) mutants of cyanobacteria, and may serve as an important adaptive mechanism for cyanobacterial survival.
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