GENETIC-ENGINEERING OF HARVEST INDEX IN TOBACCO THROUGH OVEREXPRESSION OF A PHYTOCHROME GENE

The phytochrome photoreceptor family regulates plant architecture in r esponse to environmental light signals. Phytochromes mediate the shade avoidance syndrome, in which plants react to far-red radiation reflec ted from neighbors by elongation growth, occurring at the expense of l eaf and storage organ production. We show that transgenic overproducti on of phytochrome A in tobacco suppresses shade avoidance, causing pro ximity-conditional dwarfing. At high densities in the field, assimilat es show an enhanced allocation to leaves, with a concomitant increase in harvest index. Transfer of this approach to other crop plants could provide significant improvements in productivity.