Running Head: Rht-B1c contains a new TRIM insertion

85 Dominance, semidominance and recessiveness are important modes of Mendelian inheritance. 86 The phytohormone gibberellin (GA) regulates many plant growths and developmental processes. 87 The previously cloned semidominant GAI (GA-insensitive) genes Rht1 and Rht2 in wheat were 88 the basis of the 'green revolution'. However, no completely dominant GAI gene has been cloned. 89 Here, we report molecular characterization of Rht-B1c, a dominant GAI allele in wheat, which 90 confers more extreme characteristics than its incompletely dominant alleles. Rht-B1c is caused 91 by a TRIM (terminal repeat retro-transposons in miniature) insertion in the DELLA domain. 92 Yeast two-hybrid (Y2H) assays showed that Rht-B1c protein fails to interact with GID1, thereby 93 blocking GA responses and resulting in extreme dwarfism and pleiotropic effects. By contrast 94 Rht-B1b protein only reduces interaction with GID1. Furthermore, we analyzed its functions 95 using near-isogenic lines (NILs), and examined its molecular mechanisms in transgenic rice. 96 These results indicated that the affinity between GID1 and DELLA proteins is key regulation of 97 the stability of DELLA proteins, and differential interactions determine dominant and 98 semidominant gene action responded to GA. 99