Genome-wide Association Studies of Shoot Branching in Populus

Plant architecture plays a major role in determining photosynthetic light use efficiency and biomass yield. Optimal plant architecture is critical for achieving maximum carbon capture per unit land area especially when plants are grown in high-density stands. Among various phenotypic traits, shoot branching is a key determinant of plant architecture. Substantial progress has been made in understanding the genetic control of shoot branching in herbaceous plants in the last decade. For example, recent studies in Arabidopsis, pea, rice and petunia have demonstrated that a new class of plant hormones, strigolactones, act as long-distance signaling molecules that are transported from roots to shoots to exert functional control on shoot branching. However, little is known about the genetic control of shoot branching in woody, perennial plants, which are typically several orders of magnitude taller than annual herbaceous plants. Populus has become a model woody and bioenergy crop. We conducted a genome-wide association study of shoot branching utilizing >1,000 Populus trichocarpa natural variants. Our studies have yielded numerous loci highly associated with shoot branching. Molecular and biochemical characterization of these regulators will provide new insights into the mechanism of shoot branching and facilitate the selection and production of desired Populus feedstocks for lignocellulosic biofuel production.