Submitted to: Photosynthesis Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/1/2006
Publication Date: 6/1/2006
Citation: Gong, P., Wu, G., Ort, D.R. 2006. Slow dark deactivation of Arabidopsis chloroplast ATP synthase caused by a mutation in a nonplastic SAC domain protein. Photosynthesis Research. 88:133-142. Interpretive Summary: The regulation of key enzymes in photosynthesis by light is a central factor in ensuring efficient energy storage in the rapidly changing light environment of natural habitats. The chloroplast coupling factor is one of the important enzymes regulated by light ensuring that ATP synthesis can occur efficiently when amble light is available but preventing the wasteful hydrolysis of ATP at night or when light is very low. There are still central features about the light-regulation of coupling factor activity that remained to be established and mutants of the light regulation process is one useful approach to further understand this process in leaves. In this paper we report on the cloning of mutation that interferes with the normal light regulation of development of coupling factor activity showing that is located in a protein that is involved in phosphoinositidie signaling. This study is relevant to agricultural and plant scientists interested in the regulation of photosynthesis by light.
Technical Abstract: A recessive mutant of Arabidopsis showed anomalous ATP synthase activation/deactivation characteristics as well as a distinct growth phenotype compared to the wild type. The most significant feature of this mutant is that the deactivation of ATP synthase induced by dark adaptation is very slow, indicating interference with ATP synthase regulation. Physical mapping delimited the mutation to a region in a pair of bacterial artificial chromosomes clones T16L24 and F24G16. T-DNA insertion mutants of all 34 putative genes located in this region were analyzed, and two homozygous T-DNA mutant lines of the same gene, At3g59770, had phenotypes indistinquishable from the mutant. Sequence analysis revealed a point mutation of G to A producing an amino acid substitution from Trp to Stop, thereby coding a truncated protein. At3g59770 encodes a protein with a SAC domain, a WW domain, and an ATP/GTP-binding site motif A and is known as SAC9. RT-PCR was used to amplify gene specific fragments and showed that the T-DNA mutants did not have full length transcripts whereas the point mutant fully transcribed the mutated mRNA. The RNA expression levels of the At3g59770 gene in different tissues of wild type plants were further investigated by real-time PCR showing that expression was highest in the leaves. No direct explanation of how dysfunction of the SAC 9 protein interferes with ATP synthase deactivation is apparent but may involve alteration in phosphoinositidies signaling inducing a stress mimicry response.