The karrikin signaling regulator SMAX1 controls Lotus japonicus root and root hair development by suppressing ethylene biosynthesis

An evolutionarily ancient plant hormone receptor complex comprising the α/β-fold hydrolase receptor KARRIKIN INSENSITIVE 2 (KAI2) and the F-box protein MORE AXILLARY GROWTH 2 (MAX2) mediates a range of developmental responses to smoke-derived butenolides called karrikins (KARs) and to yet elusive endogenous KAI2 ligands (KLs). Degradation of SUPPRESSOR OF MAX2 1 (SMAX1) after ligand perception is considered to be a key step in KAR/KL signaling. However, molecular events which regulate plant development downstream of SMAX1 removal have not been identified. Here we show that Lotus japonicus SMAX1 is specifically degraded in the presence of KAI2 and MAX2 and plays an important role in regulating root and root hair development. smax1 mutants display very short primary roots and elongated root hairs. Their root transcriptome reveals elevated ethylene responses and expression of ACC Synthase 7 (ACS7), which encodes a rate-limiting enzyme in ethylene biosynthesis. smax1 mutants release increased amounts of ethylene and their root phenotype is rescued by treatment with ethylene biosynthesis and signaling inhibitors. KAR treatment induces ACS7 expression in a KAI2-dependent manner and root developmental responses to KAR treatment depend on ethylene signaling. Furthermore, in Arabidopsis, KAR-induced root hair elongation depends on ACS7. Thus, we reveal a connection between KAR/KL and ethylene signaling in which the KAR/KL signaling module (KAI2–MAX2–SMAX1) regulates the biosynthesis of ethylene to fine-tune root and root hair development, which are important for seedling establishment at the beginning of the plant life cycle

The karrikin signaling regulator SMAX1 controlsLotus japonicusroot and root hair development by suppressing ethylene biosynthesis

An evolutionarily ancient plant hormone receptor complex comprising the α/β-fold hydrolase receptor KARRIKIN INSENSITIVE 2 (KAI2) and the F-box protein MORE AXILLARY GROWTH 2 (MAX2) mediates a range of developmental responses to smoke-derived butenolides called karrikins (KARs) and to yet elusive endogenous KAI2 ligands (KLs). Degradation of SUPPRESSOR OF MAX2 1 (SMAX1) after ligand perception is considered to be a key step in KAR/KL signaling. However, molecular events which regulate plant development downstream of SMAX1 removal have not been identified. Here we show that Lotus japonicus SMAX1 is specifically degraded in the presence of KAI2 and MAX2 and plays an important role in regulating root and root hair development. smax1 mutants display very short primary roots and elongated root hairs. Their root transcriptome reveals elevated ethylene responses and expression of ACC Synthase 7 (ACS7), which encodes a rate-limiting enzyme in ethylene biosynthesis. smax1 mutants release increased amounts of ethylene and their root phenotype is rescued by treatment with ethylene biosynthesis and signaling inhibitors. KAR treatment induces ACS7 expression in a KAI2-dependent manner and root developmental responses to KAR treatment depend on ethylene signaling. Furthermore, in Arabidopsis, KAR-induced root hair elongation depends on ACS7. Thus, we reveal a connection between KAR/KL and ethylene signaling in which the KAR/KL signaling module (KAI2–MAX2–SMAX1) regulates the biosynthesis of ethylene to fine-tune root and root hair development, which are important for seedling establishment at the beginning of the plant life cycle

KARRIKIN INSENSITIVE2 regulates leaf development, root system architecture and arbuscular‐mycorrhizal symbiosis in Brachypodium distachyon

International audienceKarrikins, of which KAR1 and KAR2 are representatives, are a class of abiotic plant growth regulators produced from the partial combustion of plant material (Flematti et al., 2004; Flematti et al., 2009). Released into the soil following wildfires, karrikins can promote seed germination and seedling photomorphogenesis, and thereby facilitate the revegetation process (Nelson et al., 2009; Nelson et al., 2010; Stevens et al., 2007). The butenolide moiety of karrikins is also an essential structural feature of strigolactones (SLs), which are carotenoid-derived plant hormones that regulate a range of developmental processes in plants, and also serve as a rhizosphere signal for arbuscular mycorrhizal fungi and root parasitic weeds (Waters et al., 2016; Bürger and Chory, 2020). Collectively, these butenolides possess wide-ranging biological activities with considerable agricultural and environmental significance

KARRIKIN INSENSITIVE2 regulates leaf development, root system architecture and arbuscular‐mycorrhizal symbiosis in Brachypodium distachyon

International audienceKarrikins, of which KAR1 and KAR2 are representatives, are a class of abiotic plant growth regulators produced from the partial combustion of plant material (Flematti et al., 2004; Flematti et al., 2009). Released into the soil following wildfires, karrikins can promote seed germination and seedling photomorphogenesis, and thereby facilitate the revegetation process (Nelson et al., 2009; Nelson et al., 2010; Stevens et al., 2007). The butenolide moiety of karrikins is also an essential structural feature of strigolactones (SLs), which are carotenoid-derived plant hormones that regulate a range of developmental processes in plants, and also serve as a rhizosphere signal for arbuscular mycorrhizal fungi and root parasitic weeds (Waters et al., 2016; Bürger and Chory, 2020). Collectively, these butenolides possess wide-ranging biological activities with considerable agricultural and environmental significance