Sll1252 Coordinates Electron Transport between Plastoquinone and Cytochrome b6/f Complex in Synechocystis PCC 6803.

A mutant, Δsll1252ins, was generated to functionally characterize Sll1252. Δsll1252ins exhibited a slow-growth phenotype at 70 µmol photons m-2 s-1 and glucose sensitivity. In Δsll1252ins, the rate of PSII activity was not affected, whereas the whole chain electron transport activity was reduced by 45%. The inactivation of sll1252 led to the upregulation of genes, which were earlier reported to be induced in DBMIB-treated wild-type, suggesting that Sll1252 may be involved in electron transfer from the reduced-PQ pool to Cyt b6/f. The inhibitory effect of DCMU on PSII activity was similar in both wild-type and Δsll1252ins. However, the concentration of DBMIB for 50% inhibition of whole chain electron transport activity was 140 nM for Δsll1252ins and 300 nM for wild-type, confirming the site of action of Sll1252. Moreover, the elevated level of the reduced-PQ pool in Δsll1252ins supports that Sll1252 functions between the PQ pool and Cyt b6/f. Interestingly, we noticed that Δsll1252ins reverted to wild-type phenotype by insertion of natural transposon, ISY523, at the disruption site. Δsll1252-Ntrn, expressing only the C-terminal region of Sll1252, exhibited a slow-growth phenotype and disorganized thylakoid structure compared to wild-type and Δsll1252-Ctrn (expressing only the N-terminal region). Collectively, our data suggest that Sll1252 regulates electron transfer between the PQ pool and the Cyt b6/f complex in the linear photosynthetic electron transport chain via coordinated function of both the N- and C-terminal regions of Sll1252.

A membrane-bound cAMP receptor protein, SyCRP1 mediates inorganic carbon response in Synechocystis sp. PCC 6803.

The availability of inorganic carbon (Ci) as the source for photosynthesis is fluctuating in aquatic environments. Despite the involvement of transcriptional regulators CmpR and NdhR in regulating genes encoding Ci transporters at limiting CO2, the Ci-sensing mechanism is largely unknown among cyanobacteria. Here we report that a cAMP-dependent transcription factor SyCRP1 mediates Ci response in Synechocystis. The mutant ∆sycrp1 exhibited a slow-growth phenotype and reduced maximum rate of bicarbonate-dependent photosynthetic electron transport (Vmax) compared to wild-type at the scarcity of CO2. The number of carboxysomes was decreased significantly in the ∆sycrp1 at low CO2 consistent with its reduced Vmax. The DNA microarray analysis revealed the upregulation of genes encoding Ci transporters in ∆sycrp1. The membrane-localized SyCRP1 was released into the cytosol in wild-type cells shifted from low to high CO2 or upon cAMP treatment. Soluble His-tagged SyCRP1 was shown to target DNA-binding sites upstream of the Ci-regulated genes sbtA and ccmK3. In addition, cAMP enhanced the binding of SyCRP1 to its target sites. Our data collectively suggest that the Ci is sensed through the second messenger cAMP releasing membrane-bound SyCRP1 into cytoplasm under sufficient CO2 conditions. Hence, SyCRP1 is a possible regulator of carbon concentrating mechanism, and such a regulation might be mediated via sensing Ci levels through cAMP in Synechocystis.

Four new Bent-toed geckos (Cyrtodactylus Gray: Squamata: Gekkonidae) from northeast India.

Based on morphology and ND2 gene sequences, four new species of Cyrtodactylus, two each from the Indian states of Meghalaya and Mizoram are described herein. The new species are a part of the Cyrtodactylus khasiensis group. The species from Meghalaya represent the lowland clade whereas the species from Mizoram represent the highland clade within the south of Brahmaputra clade of Indo-Burmese Cyrtodactylus. The two distinct populations from Meghalaya are sister to one another, differing from each by an uncorrected p-distance 0.065 and collectively are sister to Cyrtodactylus septentrionalis. The species from Mizoram differ from each other by an uncorrected p-distance of 0.0850.121 and collectively are sister to Cyrtodactylus montanus.