Ectopic Expression of a Transmembrane Protein KaCyt B6from a Red SeaweedKappaphycus Alvareziiin Transgenic Tobacco Augmented the Photosynthesis and Growth

Cytochrome b(6)f complex is a thylakoid membrane-localized protein and catalyses the transfer of electrons from plastoquinol to plastocyanin in photosynthetic electron transport chain. In the present study,Cytochrome b(6)(KaCyt b(6)) gene fromKappaphycus alvarezii(a red seaweed) was overexpressed in tobacco. A 935 base pair (bp) longKaCyt b(6)cDNA contained an open reading frame of 648 bp encoding a protein of 215 amino acids with an expected isoelectric point of 8.67 and a molecular mass of 24.37 kDa. TheKaCyt b(6)gene was overexpressed in tobacco under control of CaMV35S promoter. The transgenic tobacco had higher electron transfer rate and photosynthetic yield over wild-type and vector control tobacco. TheKaCyt b(6)tobacco also exhibited significantly higher photosynthetic gas exchange (P-N) and improved water use efficiency. The transgenic plants had higher ratio of P(N)and intercellular CO2. TheKaCyt b(6)transgenic tobacco showed higher estimates of photosystem II quantum yield, higher activity of the water-splitting complex, PSII photochemistry, and photochemical quenching. The basal quantum yield of nonphotochemical processes in PSII was recorded lower inKaCyt b(6)tobacco. Transgenic tobacco contained higher contents of carotenoids and total chlorophyll and also had better ratios of chlorophyll a and b, and carotenoids and total chlorophyll contents hence improved photosynthetic efficiency and production of sugar and starch. TheKaCyt b(6)transgenic plants performed superior under control and greenhouse conditions. To the best of our knowledge through literature survey, this is the first report on characterization ofKaCyt b(6)gene fromK. alvareziifor enhanced photosynthetic efficiency and growth in tobacco.