A novel regulator of wheat tillering LT1 identified by using an innovative BSA method

Branching/tillering is a critical process for plant architecture and grain yield. However, Branching is intricately controlled by both endogenous and environmental factors. The underlying mechanisms of tillering in wheat remain poorly understood. In this study, we identified Less Tiller 1 ( LT1 ) as a novel regulator of wheat tillering using a newly upgraded bulked segregant analysis (BSA) method called uni-BSA, which is well-suited for wheat. Loss-of-function of LT1 results in fewer tillers due to defects in axillary meristem initiation and bud outgrowth. We mapped LT1 to a 6 Mb region on the chromosome 2D short arm and validated a nucleotide-binding (NB) domain encoding gene as LT1 using CRISPR/Cas9. Furthermore, the lower sucrose concentration in the shoot bases of lt1 might result in inadequate bud outgrowth due to disturbances in the sucrose biosynthesis pathways. Co-expression analysis suggests that LT1 controls tillering by regulating TaROX/TaLAX1 , the ortholog of the Arabidopsis tiller regulator REGULATOR OF AXILLARY MERISTEM FORMATION ( ROX ) or the rice axillary meristem regulator LAX PANICLE1 ( LAX1 ). This study not only offers a novel genetic resource for cultivating optimal plant architecture but also underscores the importance of our innovative BSA method. This uni-BSA method enables the swift and precise identification of pivotal genes associated with significant agronomic traits, thereby hastening gene cloning and crop breeding processes in wheat.