Investigating the Genetic Control of Shoot Lateral Branching in Barley

Barley is an internationally important crop for malting, brewing, and animal feed. Barley plant architecture is largely defined by the number and vigor of tillers, lateral shoots that arise from axillary meristems (AXM) at the plant base. The majority of grain yield in barley comes from tillers, but the genetic and developmental control underlying tiller growth is still largely unknown. This study aims to 1) identify natural genetic variation affecting tiller growth through genome-wide association mapping, 2) better understand how other traits affect and are affected by tiller number, and 3) identify genes differentially expressed in AXM and shoot apical meristems (SAM) that influence tiller growth. For the first two aims, a subset of the USDA National Small Grains iCore Collection was field-grown in Saint Paul, MN in 2014 and 2015. Lines were genotyped using ~55,000 Tag SNPs that were used for association mapping and population structure analysis. Data for heading date, weekly tiller number per plant, and numerous other traits were collected throughout development. Mixed linear modeling and correlations between tiller growth and other traits indicate that tiller growth is pleiotropically influenced by other traits, such as flowering time and number of seeds per spike. The pleiotropic influence of flowering time on tiller growth was further demonstrated by extensive overlap (>70%) of tiller growth and flowering time QTL. For the third aim, Laser Microdissection-RNAseq analysis of SAM and AXM from two Bowman seedling stages revealed differentially expressed genes overlapping tiller growth QTL that may potentially influence tiller growth.