Ectopic expression of Arabidopsis phytochrome B in Troyer citrange affects photosynthesis and plant morphology

Phytochromes are photoreceptors that regulate signal transduction of metabolic pathways and plant development in response to changes in environmental light quality and levels. Studies have shown that mutant plants deficient in phytochromes and transgenic plants overexpressing phytochrome genes exhibit altered canopy growth characteristics. Troyer citrange was transformed with a binary vector system of Agrobacterium tumefaciens carrying the neomycin phosphotransferase II (nptII) and Arabidopsis thaliana phytochrome B (PHYB) gene. Three transgenic lines were used to investigate the influence of overexpression of phytochrome B on fruit tree plant development through morphological and physiological analyses in addition to gene expression analyses. All the regenerated transgenic plants showed altered physiological and architectural canopy development compared with wild-type plants. In particular PHYB1 transgenic clone was further characterized under particular growing conditions and molecular analysis was used to study the effect of the transgene on gene expression during photosynthesis. The expression of chloroplast and nuclear genes that are directly involved in the light and dark phases of photosynthesis was found to be particularly enhanced in the transgenic plant.