A Tripartite Amplification Loop Involving the Transcription Factor WRKY75, Salicylic Acid, and Reactive Oxygen Species Accelerates Leaf Senescence

Abstract

Leaf senescence is a highly coordinated, complicated process involving the integration of numerous internal and environmental signals. Salicylic acid (SA) and reactive oxygen species (ROS) are two well-defined inducers of leaf senescence whose contents progressively and interdependently increase during leaf senescence via an unknown mechanism. Here, we characterized the transcription factor WRKY75 as a positive regulator of leaf senescence in Knockdown or knockout of delayed age-dependent leaf senescence, while overexpression of accelerated this process. transcription is induced by age, SA, HO, and multiple plant hormones. Meanwhile, WRKY75 promotes SA production by inducing the transcription of () and suppresses HO scavenging, partly by repressing the transcription of (). Genetic analysis revealed that the mutation of or an increase in catalase activity rescued the precocious leaf senescence phenotype evoked by overexpression. Based on these results, we propose a tripartite amplification loop model in which WRKY75, SA, and ROS undergo a gradual but self-sustained rise driven by three interlinking positive feedback loops. This tripartite amplification loop provides a molecular framework connecting upstream signals, such as age and plant hormones, to the downstream regulatory network executed by SA- and HO-responsive transcription factors during leaf senescence.

Disruption of Arabidopsis neutral ceramidases 1 and 2 results in specific sphingolipid imbalances triggering different phytohormone‐dependent plant cell death programmes

“…21‐fold in ncer2 and ncer1 ncer2 mutants (Fig. b; Guo et al ., ; Zhang et al ., ). Moreover, the expression of NONEXPRESSOR OF PATHOGENESIS‐RELATED GENES 1 ( NPR1 ) gene, encoding a positive regulator of the SA‐dependent basal resistance pathway was slightly elevated in all ncer mutants.…”

“…It is well known that SA triggers the upregulation of several SAG genes and thereby promotes leaf senescence (Morris et al ., ; Jing et al ., ). In addition, SA biosynthesis and signalling mutants such as sid2‐2 exhibit delayed leaf senescence phenotypes (Guo et al ., ). Our results provide further evidence for the importance of SA in the regulation of leaf senescence as the sid2 mutation completely abolished the early senescence phenotype of the ncer1 and ncer1 ncer2 mutants (Fig.…”

“…). Recently, it was proposed that the WRKY75 transcription factor induces the transcription of SID2, which leads to accumulation of SA and H 2 O 2 and finally promotes leaf senescence and bacterial resistance in Arabidopsis (Guo et al ., ). Our analysis supports this model, as the expression of WRKY75 is upregulated in the ncer2 and ncer1 ncer2 mutants (Fig.…”

“…We found that WRKY75, a positive regulator of SID2 transcription during leaf senescence and New Phytologist the plant defence response, is upregulated c. six-fold and c. 21fold in ncer2 and ncer1 ncer2 mutants ( Fig. 6b; Guo et al, 2017;Zhang et al, 2017). Moreover, the expression of NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1) gene, encoding a positive regulator of the SA-dependent basal resistance pathway was slightly elevated in all ncer mutants.…”

The long noncoding RNA T5120 regulates nitrate response and assimilation in Arabidopsis

“…Protoplasts were isolated according to Sheen (http://genetics.mgh.harvard.edu/ sheenweb) as described previously (Li et al, 2005). Protoplasts were cotransfected with pT5120::LUC and p35S::NLP7 or pT5120:: LUC and empty vector and incubated under dark conditions for 16 h. The firefly luciferase/Renilla luciferase (LUC/REN) ratio was monitored following the protocol of the TransDetect Double-Luciferase Reporter Assay Kit (TransGen Biotech, Beijing, China) using a luminometer (Promega) as previously described (Guo et al, 2017). All primers used here are listed in Table S1.…”