Abstract
Plants contain an extensive family of PsbP-related proteins termed PsbP-like (PPL) and PsbP domain (PPD) proteins, which are localized to the thylakoid lumen. The founding member of this family, PsbP, is an established component of the Photosystem II (PS II) enzyme, and the PPL proteins have also been functionally linked to other photosynthetic processes. However, the functions of the remaining seven PPD proteins are unknown. To elucidate the function of the PPD5 protein (At5g11450) in Arabidopsis, we have characterized a mutant T-DNA insertion line (SALK_061118) as well as several RNAi lines designed to suppress the expression of this gene. The functions of the photosynthetic electron transfer reactions are largely unaltered in the ppd5 mutants, except for a modest though significant decrease in NADPH dehydrogenase (NDH) activity. Interestingly, these mutants show striking plant developmental and morphological defects. Relative to the wild-type Col-0 plants, the ppd5 mutants exhibit both increased lateral root branching and defects associated with axillary bud formation. These defects include the formation of additional rosettes originating from axils at the base of the plant as well as aerial rosettes formed at the axils of the first few nodes of the shoot. The root-branching phenotype is chemically complemented by treatment with the synthetic strigolactone, GR24. We propose that the developmental defects observed in the ppd5 mutants are related to a deficiency in strigolactone biosynthesis.
Highlights
The thylakoid membranes of plant chloroplasts contain the enzymes responsible for the photosynthetic reactions that convert solar energy into biochemical energy and molecular oxygen
The numerous introns and exons within the PPD5 gene and the fact that the TDNA insertion was located near the 39 end of the gene raised the possibility that alternative transcripts could be present in the ppd5 mutant, either as chimeric transcripts, truncated transcripts or alternatively spliced forms
Transcripts for the other PsbP family members (PSBP, PPL1-2, and PPD1-4, and 6) were detected in the PPD5 RNAi lines, indicating that PPD5 is suppressed in these plants
Summary
The thylakoid membranes of plant chloroplasts contain the enzymes responsible for the photosynthetic reactions that convert solar energy into biochemical energy and molecular oxygen. The thylakoid membranes contain light-harvesting antenna complexes (LHCI and LHCII), chaperones for membrane protein integration, translocation complexes for targeting of lumenal proteins, NADPH dehydrogenase complexes (NDH), and a plastid terminal oxidase (PTOX) [1]. These molecular machines, in concert with an extensive network of regulators and factors required for biogenesis, collectively maintain optimal electron transfer. PsbP is essential for autotrophy in both land plants [5,6] and green algae [7,8] and is required for normal thylakoid architecture in Arabidopsis [9]
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