A Soybean Dual-Specificity Kinase, GmSARK, and Its Arabidopsis Homolog, AtSARK, Regulate Leaf Senescence through Synergistic Actions of Auxin and Ethylene      

Abstract

As the last stage of leaf development, senescence is a fine-tuned process regulated by interplays of multiple signaling pathways. We have previously identified soybean (Glycine max) SENESCENCE-ASSOCIATED RECEPTOR-LIKE KINASE (SARK), a leucine-rich repeat-receptor-like protein kinase from soybean, as a positive regulator of leaf senescence. Here, we report the elucidation of the molecular mechanism of GmSARK-mediated leaf senescence, especially its specific roles in senescence-inducing hormonal pathways. A glucocorticoid-inducible transcription system was used to produce transgenic Arabidopsis (Arabidopsis thaliana) plants for inducible overexpression of GmSARK, which led to early leaf senescence, chloroplast destruction, and abnormal flower morphology in Arabidopsis. Transcript analyses of the GmSARK-overexpressing seedlings revealed a multitude of changes in phytohormone synthesis and signaling, specifically the repression of cytokinin functions and the induction of auxin and ethylene pathways. Inhibition of either auxin action or ethylene biosynthesis alleviated the senescence induced by GmSARK. Consistently, mutation of either AUXIN RESISTANT1 or ETHYLENE INSENSITIVE2 completely reversed the GmSARK-induced senescence. We further identified a homolog of GmSARK with a similar expression pattern in Arabidopsis and named it AtSARK. Inducible overexpression of AtSARK caused precocious senescence and abnormal floral organ development nearly identical to the GmSARK-overexpressing plants, whereas a T-DNA insertion mutant of AtSARK showed significantly delayed senescence. A kinase assay on recombinant catalytic domains of GmSARK and AtSARK revealed that these two leucine-rich repeat-receptor-like protein kinases autophosphorylate on both serine/threonine and tyrosine residues. We inferred that the SARK-mediated pathway may be a widespread mechanism in regulating leaf senescence.

Plant leaf senescence and death – regulation by multiple layers of control and implications for aging in general

“…However, the exact mechanism by which RPK1 receives and transduces senescence signals to its targets to regulate leaf senescence requires further investigation. Soybean (Glycine max) SENESCENCE-ASSOCIATED RECEPTOR-LIKE KINASE (GmSARK) and its Arabidopsis homolog (AtSARK) were shown to be positive regulators of leaf senescence (Xu et al,2011). The authors found that GmSARK-overexpressing Arabidopsis plants exhibit altered responses to multiple hormones, such as ethylene, auxin and cytokinin.…”

SENESCENCE-SUPPRESSED PROTEIN PHOSPHATASE Directly Interacts with the Cytoplasmic Domain of SENESCENCE-ASSOCIATED RECEPTOR-LIKE KINASE and Negatively Regulates Leaf Senescence in Arabidopsis

“…We previously reported that a soybean (Glycine max) dual-specificity kinase, GmSARK, and its Arabidopsis homolog, AtSARK, regulate leaf senescence through the synergistic actions of auxin and ethylene (Xu et al, 2011). In this study, we cloned and identified a PP2C-type protein phosphatase, SENESCENCE-SUPPRESSED PROTEIN PHOSPHATASE (SSPP), which negatively regulates leaf senescence in Arabidopsis.…”

An Abscisic Acid-AtNAP Transcription Factor-SAG113 Protein Phosphatase 2C Regulatory Chain for Controlling Dehydration in Senescing Arabidopsis Leaves

“…111.190876 senescence processes induced by various factors share common execution events but different hormonal, pathological, or environmental signals that lead to initiation of senescence may do so through distinct signal transduction pathways (Guo and Gan, 2012). More than 200 genes coding for components of several signal transduction pathways are associated with the processes, including the mitogen-activated protein kinase pathways, G proteins, Ca 2+ -dependent protein kinases, receptor-like kinases, calmodulins, and protein phosphatase (PP) 2A and 2C (Hajouj et al, 2000;Guo et al, 2004;Zhou et al, 2009;Xu et al, 2011). Protein kinases and phosphatases add or remove phosphate groups from proteins, respectively, to relay signals to modulate various biochemical and molecular processes.…”