Physical interaction between ARR1 and DELLAs regulates division at the root meristem and photomorphogenesis.

(A) Root meristem size of 35S::ARR1ΔDDK:GR seedlings grown for 4 days with and without GAs. (n = 20; data are mean ± SD, ***p<0.001 in a Student’s t-test with respect to control plants). Arrowheads mark the extension of the meristem. (B) Angle between cotyledons of 35S::ARR1ΔDDK:GR seedlings grown for 4 days with and without GAs in darkness. (n = 18; data are mean ± SD; ***p<0.001 in a Student’s t-test with respect to seedlings treated with DEX without GAs). (C) Angle between cotyledons of 35S::ARR1ΔDDK:GR seedlings in gai rga double mutant or in an otherwise wild-type background. Seedlings were grown for 4 days in darkness. (n = 15; data are mean ± SD; ***p<0.001 in a Student’s t-test with respect to 35S::ARR1ΔDDK:GR GAI RGA seedlings treated with DEX). (D) Angle between cotyledons of wild-type and arr1 arr12 seedlings grown for 4 days with and without PAC in darkness. (n = 18; data are mean ± SD; ***p<0.001 in a Student’s t-test with respect to PAC-treated wild-type seedlings). Experiments were performed as indicated in Materials and Methods. Equivalent treatments of wild-type seedlings with DEX did not cause any change in root meristem size and or the angle between cotyledons.