PIN-LIKES coordinate brassinosteroid signalling with nuclear auxin input in Arabidopsis thaliana

Abstract

Auxin and brassinosteroids (BR) are crucial growth regulators and display overlapping functions during plant development. Here, we reveal an alternative phytohormone crosstalk mechanism, revealing that brassinosteroid signaling controls nuclear abundance of auxin. We performed a forward genetic screen for imperial pils (imp) mutants that enhance the overexpression phenotypes of PIN-LIKES (PILS) putative intracellular auxin transport facilitator. Here we report that the imp1 mutant is defective in the brassinosteroid-receptor BRI1. Our data reveals that BR signaling transcriptionally and posttranslationally represses accumulation of PILS proteins at the endoplasmic reticulum, thereby increasing nuclear abundance and signaling of auxin. We demonstrate that this alternative phytohormonal crosstalk mechanism integrates BR signaling into auxin-dependent organ growth rates and likely has widespread importance for plant development.