ABI3 promotes auxin signalling by regulating SHY2 expression to control primary root growth in response to dehydration stress

Abstract

Plants combat dehydration stress through several adaptive measures including root architectural changes. Here we show that when exposed to varying levels of dehydration stress, primary root growth in Arabidopsis is modulated by regulating root meristem activity. ABA in concert with auxin signalling perceives the stress level and adapts primary root growth accordingly. ABI3, the ABA responsive transcription factor stands at the intersection of ABA and auxin signalling and fine tunes primary root growth in response to dehydration stress. Under low ABA or dehydration stress, induction of ABI3 expression promotes auxin signalling by decreasing expression of SHY2, a negative regulator of auxin response. This further enhances the expression of auxin transporter gene PIN1 and cell cycle gene CYCB1;1, resulting in an increase in primary root meristem size and root length. Higher levels of dehydration stress or ABA repress ABI3 expression and promote ABI5 expression. This elevates SHY2 expression, thereby impairing primary root meristem activity and retarding root growth. Notably, ABI5 can promote SHY2 expression only in the absence of ABI3. Such ABA concentration dependent expression of ABI3 therefore functions as a regulatory sensor of dehydration stress levels and orchestrates primary root growth by coordinating its downstream regulon.

Keywords: ABA; ABI3; ABI5; Dehydration stress; SHY2; primary root; root meristem.