PpSARK Regulates Moss Senescence and Salt Tolerance through ABA Related Pathway

Abstract

Senescence-associated receptor-like kinase (SARK) family members in Arabidopsis, soybean, and rice are known to be positive regulators of leaf senescence. In the meantime, SARKs are extensively involved in stress response. However, their function and underlying molecular mechanism in stress responses in moss are not well known. Here, we investigated functional roles of SARK isolated from Physcomitrella patens (PpSARK) in salt stress response and senescence. PpSARK transcripts significantly accumulated under NaCl and abscisic acid (ABA) treatments, with higher expression in the moss gametophyte stage. Insertional gain-of-function mutants of PpSARK (PpSARKg) were more tolerant to salt stress and ABA than wild type (WT), whereas senescence of mutants was delayed during the protonema stage. Expression of stress-responsive genes in the ABA related pathway, such as PpABI3, PpABI5, PpPP2C, and PpLEA were significantly higher in PpSARKg and WT under salt stress conditions, suggesting that PpSARK might positively regulate salt tolerance via an ABA-related pathway. Endogenous ABA contents also increased 3-fold under salt stress conditions. These results indicate that PpSARK functions as a positive regulator in salt stress responses, while possibly functioning as a negative regulator in senescence in moss.

A Review on Plant Responses to Salt Stress and Their Mechanisms of Salt Resistance

“…ABA does not act directly, but through inducing these AREBs, thus it is believed that overexpressing these AREBs can enhance plants' tolerance to abiotic stress. Li et al suggested that PpSARK (Senescence-associated receptorlike kinase) functions as a positive regulator in salt stress responses through an ABA-related pathway in Physcomitrella patens [175]. Zhang and his team found that OsNAC45 plays a key role in ABA signal responses and salt tolerance in rice [176].…”

“…Arabidopsis thaliana null function in the root fine-tuning the redox homeostasis [196] PpSARK Physcomitrella patens null senescence-associated receptor-like kinase related to ABA [175] GmTIP2;3 Glycine max null a tonoplast intrinsic protein related to osmotic regulation [140] VvNAC17…”

Stress, senescence, and specialized metabolites in bryophytes

“…What exists is limited to preliminary studies on general signalling pathways or information on specific cells undergoing programmed senescence, such as mucilage or stomatal cells ( Renzaglia et al , 2017 ). Potential regulatory genes have been identified relating to some hormone pathways, specifically for abscisic acid-induced senescence in P. patens ( Li et al , 2018 ) and jasmonate responses in M. polymorpha ( Monte et al , 2019 ). Nitrogen or phosphate starvation of M. polymorpha has been shown to induce flavonoid pigmentation via R2R3MYB-mediated gene activation ( Albert et al , 2018 ; Kubo et al , 2018 ; Rico-Reséndiz et al , 2020 ).…”

Function of Protein Kinases in Leaf Senescence of Plants

“…A LRR-RLK from bean ( Phaseolus vulgaris ) was named senescence-associated receptor-like kinase (SARK) because its mRNA and protein levels increased during leaf senescence ( Hajouj et al, 2000 ). PpSARK ( Physcomitrella patens senescence-associated receptor-like kinase), with high homology to the bean SARK, is involved in the regulation of moss ( Physcomitrella patens ) senescence ( Li et al, 2018 ). Another LRR-RLK gene involved in the regulation of leaf senescence was isolated in the soybean ( Glycine max ) and named Glycine max senescence-associated receptor-like kinase (GmSARK).…”