Alteration of expression in species leads to pleiotropic shoot phenotypes.

(peach) trees carrying the "Pillar" or "Broomy" trait () have vertically oriented branches caused by loss-of-function mutations in a gene called (). encodes a protein in the IGT gene family that includes and (), which regulate lateral branch and root orientations, respectively. Here we found that some of the native alleles in the hexaploid plum species , which has a naturally more upright stature, contained a variable length trinucleotide repeat within the same exon 3 region previously found to be disrupted in pillar peach trees. RNAi silencing of in plum resulted in trees with severely vertical branch orientations similar to those in pillar peaches but with an even narrower profile. In contrast, overexpression in plum led to trees with wider branch angles and more horizontal branch orientations. Pillar peach trees and transgenic plum lines exhibited pleiotropic phenotypes, including differences in trunk and branch diameter, stem growth, and twisting branch phenotypes. Expression profiling of pillar peach trees revealed differential expression of numerous genes associated with biotic and abiotic stress, hormone responses, plastids, reactive oxygen, secondary, and cell wall metabolism. Collectively, the data provide important clues for understanding function and show that alteration of expression may have broad applicability to agricultural and ornamental tree industries.