KAI2-dependent signaling controls vegetative reproduction inMarchantia polymorphathrough activation of LOG-mediated cytokinin synthesis

Abstract

AbstractMarchantia polymorphareproduces vegetatively (asexually) by producing propagules known as gemmae within gemma cups and sexually through spores. We previously reported that KARRIKIN INSENSITIVE 2 (KAI2)-dependent signaling promotes gemma cup and gemma formation. KAI2A perceives unidentified endogenous ligand(s), tentatively referred to as KAI2 ligands (KL). Perception of KL by KAI2 triggers MAX2-dependent proteolysis of MpSMXL. In this study, we identified genes working downstream of KAI2-dependent signaling inM. polymorpha. We found that KAI2-dependent signaling positively controls the expression of MpLONLEY GUY(MpLOG), encoding a cytokinin biosynthesis enzyme. Disruption of the MpLOGfunction decreased endogenous cytokinin levels and caused defects similar to KAI2-dependent signaling mutants. Moreover, supplying exogenous cytokinins rescued the defects of Mplogand KAI2-dependent signaling mutants, implying that cytokinins work downstream of KAI2-dependent signaling. Activation of MpLOGby KAI2-dependent signaling occurs in a highly cell-type-specific manner, leading to cell-specific induction ofGEMMA CUP-ASSOCIATED MYB1(GCAM1), the master regulator of vegetative reproduction ofM. polymorpha. We propose a genetic cascade, starting from KAI2-dependent signaling, that promotes vegetative reproduction through the induction of MpLOGandGCAM1. The interaction between KAI2-dependent signaling and cytokinin inM. polymorphaprovides a novel insight into the function and evolution of KAI2-dependent signaling.