Chloroplast-encoded chlB gene from Pinus thunbergii promotes root and early chlorophyll pigment development in Nicotiana tabaccum

Abstract

Chlorophyll biosynthesis is catalyzed by two multi subunit enzymes; a light-dependent and a light-independent protochlorophyllide oxidoreductase. The light-independent enzyme consists of three subunits (ChlL, ChlN and ChlB) in photosynthetic bacteria and plastids in which the chlB gene encodes the major subunit that catalyzes the reduction of protochlorophyllide to chlorophyllide. We report here stable integration of the chlB gene from Pinus thunbergii into the chloroplast genome of tobacco. Using helium-driven biolistic gun, transplastomic clones were developed in vitro. The stable integration and homoplasmy for transgenes was confirmed by using PCR and Southern blotting techniques. Nodal cuttings of the homoplasmic transgenic and untransformed wild type shoots were cultured on MS medium in the dark. As expected, shoots developed from the cuttings of the wild type plants in the dark showed etiolated growth with no roots whereas shoots from the cuttings of the transgenic plants developed early and more roots. Upon shifting from dark to light in growth room, leaves of the transgenic shoots showed early development of chlorophyll pigments compared to the wild type shoots. Further, photosynthetically indistinguishable transgenic shoots also showed significant difference in root development from untransformed wild type shoots when cuttings were grown in the light. Therefore, it may be concluded that the chlB gene is involved, directly or indirectly, in the root development of tobacco. Further, the gene promotes early development of chlorophyll pigments, upon illumination from dark, in addition to its role in the light-independent chlorophyll formation when expressed together with subunits L&N in other organisms.