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Authors: Tsukasa Toriyama, Akihisa Shinozawa, Yuki Yasumura, Masashi Saruhashi, Mayuka Hiraide, Shiori Ito, Hideyuki Matsuura, Keiko Kuwata, Mika Yoshida, Tadashi Baba, Izumi Yotsui, Teruaki Taji, Daisuke Takezawa and Yoichi Sakata.
Current Biology (2022)
Editor's view: Toriyama et al. show that, in the moss Physcomitrium patens, ethylene-receptor- related sensor histidine kinases (HKs) interact with a Raf kinase (RAF) at the endoplasmic reticulum. This HK-RAF module is essential for ethylene-mediated submergence signaling and abscisic-acid-mediated osmostress signaling for optimal environmental stress responses.
Highlights: • Ethylene-receptor-related histidine kinases are essential for moss stress responses • ETR-HKs interact with a RAF kinase at the endoplasmic reticulum • ETR-HKs regulate ABA-dependent activation of SnRK2 via RAF kinase activation
Abstract: "To survive fluctuating water availability on land, terrestrial plants must be able to sense water stresses, such as drought and flooding. The plant hormone abscisic acid (ABA) and plant-specific SNF1-related protein kinase 2 (SnRK2) play key roles in plant osmostress responses. We recently reported that, in the moss Physcomitrium patens, ABA and osmostress-dependent SnRK2 activation requires phosphorylation by an upstream RAF-like kinase (ARK). This RAF/SnRK2 module is an evolutionarily conserved mechanism of osmostress signaling in land plants. Surprisingly, ARK is also an ortholog of Arabidopsis CONSTITUTIVE RESPONSE 1 (CTR1), which negatively regulates the ethylene-mediated submergence response of P. patens, indicating a nexus for cross-talk between the two signaling pathways that regulate responses to water availability. However, the mechanism through which the ARK/SnRK2 module is activated in response to water stress remains to be elucidated. Here, we show that a group of ethylene-receptor-related sensor histidine kinases (ETR-HKs) is essential for ABA and osmostress responses in P. patens. The intracellular kinase domain of an ETR-HK from P. patens physically interacts with ARK at the endoplasmic reticulum in planta. Moreover, HK disruptants lack ABA-dependent autophosphorylation of the critical serine residue in the activation loop of ARK, leading to loss of SnRK2 activation in response to ABA and osmostress. Collectively with the notion that ETR-HKs participate in submergence responses, our present data suggest that the HK/ARK module functions as an integration unit for environmental water availability to elicit optimized water stress responses in the moss P. patens."
