Modification of hormone signaling for improvement of plants

Plant growth and development are intricately regulated by phytohormones. Some of the key parameters that can be attributed to phytohormone regulation include vegetative biomass, branching, leaf area, seed number, and seed weight. These are traits are important for ornamental crops as well as for influencing yield parameters in agricultural crops. We explored manipulation of cytokinin signaling as an avenue for influencing these traits. We isolated and characterized a gene encoding for a cytokinin binding protein (CBP) to manipulate cytokinin signaling from Petunia hybrida (PETCBP-Petunia cytokinin binding protein), Arabidopsis thaliana (HOG1-Homology dependent gene silencing1), and rice (OsCBP-Orzya sativa Cytokinin Binding Protein). This gene is present in diverse crop species and has sequence similarity to S-adenosyl homocysteine hydrolase. Our data show that suppression of PETCBP, HOG1, or OsCBP leads to significant increase in biomass by enhanced branching or tillering. Transgenic plants overexpressing the HOG1 cDNA showed early flowering and significantly reduced number of leaves and early senescence. Profuse branching, delayed flowering, and increased leaf size and seed yield were some of the phenotypes observed in the antisense suppression lines of PETCBP and HOG1. The phenotypes were confirmed by independent studies on Nicotiana benthamiana using virus-induced gene silencing (VIGS) technique. Hence, our results show that the PETCBP gene or its orthologs may contribute to genetic improvement of various crop plants including those used for biofuels (cellulosic ethanol), leafy vegetables, and ornamentals, as well as fodder grass.