MPK3/6‐induced degradation of ARR1/10/12 promotes salt tolerance in Arabidopsis

Abstract

Cytokinins are phytohormones that regulate plant development, growth, and responses to stress. In particular, cytokinin has been reported to negatively regulate plant adaptation to high salinity; however, the molecular mechanisms that counteract cytokinin signaling and enable salt tolerance are not fully understood. Here, we provide evidence that salt stress induces the degradation of the cytokinin signaling components Arabidopsis (Arabidopisis thaliana) response regulator 1 (ARR1), ARR10 and ARR12. Furthermore, the stress‐activated mitogen‐activated protein kinase 3 (MPK3) and MPK6 interact with and phosphorylate ARR1/10/12 to promote their degradation in response to salt stress. As expected, salt tolerance is decreased in the mpk3/6 double mutant, but enhanced upon ectopic MPK3/MPK6 activation in an MKK5DD line. Importantly, salt hypersensitivity phenotypes of the mpk3/6 line were significantly alleviated by mutation of ARR1/12. The above results indicate that MPK3/6 enhance salt tolerance in part via their negative regulation of ARR1/10/12 protein stability. Thus, our work reveals a new molecular mechanism underlying salt‐induced stress adaptation and the inhibition of plant growth, via enhanced degradation of cytokinin signaling components.

Mitogen‐activated protein kinase cascades in plant signaling

“…Recently, Yan and coworkers reported that MPK3 and MPK6 interact with and phosphorylate Arabidopsis response regulator 1 (ARR1), ARR10, and ARR12, key cytokinin signaling components, to promote their degradation in response to salt stress (Yan et al, 2021). Plant salt tolerance is reduced in the mpk3 mpk6 double mutant, but enhanced upon ectopic MPK3/MPK6 activation in the GOF MKK5‐DD line.…”

Auxin/Cytokinin Antagonistic Control of the Shoot/Root Growth Ratio and Its Relevance for Adaptation to Drought and Nutrient Deficiency Stresses

“…The salt stress and drought stress responses are closely related, which is not surprising considering that salt stress leads to a reduction in water availability [103,104]. The mitogenactivated protein kinases 3 and 6 (MPK3 and MPK6) play an essential role in the salt stress response of plants, and they promote salt stress tolerance by promoting degradation of Type-B RR cytokinin response activators [105]. It is still to be determined if MPK3-and MPK6-dependent degradation of Type-B RRs plays a role in drought stress response, but if it does, it will bring to light another mechanism of drought stress-dependent suppression of cytokinin signaling.…”

CYTOKININ RESPONSE FACTOR 2 is involved in modulating the salt stress response

“…An estimated that 800 million hectares of arable land worldwide are affected by saline soils and gaining a better understanding of how plants adjust to these problems can aid in the development of ameliorative strategies (Acosta‐Motos et al., 2017). One untapped possibility to explore are the connections found between stress responses and the plant hormone cytokinin (Abdelrahman et al., 2021; Albrecht & Argueso, 2017; Keshishian et al., 2018; Yan et al., 2021; Zwack & Rashotte, 2015).…”

“…However, recently there have been a number of studies that show roles for cytokinins in stress‐related processes (Albrecht & Argueso, 2017; Zwack & Rashotte, 2015). Additionally, some studies have connected cytokinin signaling and biosynthesis to the salt stress response (Ghanem et al., 2011; Golan et al., 2016; Joshi et al., 2018; Keshishian et al., 2018; Nishiyama et al., 2011; Prerostova et al., 2017; Yan et al., 2021), yet a detailed examination of the specific genes involved in this interaction is needed. One group of cytokinin‐induced genes that has been linked to different types of abiotic stress response are the cytokinin response factors or CRFs (Gupta & Rashotte, 2014; Hallmark & Rashotte, 2019; Hughes et al., 2021; Jeon et al., 2016; Shi et al., 2012, 2014; Zwack et al., 2013; Zwack, Compton, et al., 2016; Zwack, De Clercq, et al., 2016).…”