Ring/U-Box Protein AtUSR1 Functions in Promoting Leaf Senescence Through JA Signaling Pathway in Arabidopsis.

Mengmeng Xu,Yongfeng Guo,Zenglin Zhang

doi:10.3389/fpls.2020.608589

Abstract

Leaf senescence is regulated by a large number of internal and environmental factors. Here, we report that AtUSR1 (U-box Senescence Related 1) which encodes a plant Ring/U-box protein, is involved in age-dependent and dark-induced leaf senescence in Arabidopsis. Expression of AtUSR1 gene in leaves was up-regulated in darkness and during aging. Plants of usr1, an AtUSR1 gene knock-down mutant, showed a significant delay in age-dependent and dark-induced leaf senescence and the delayed senescence phenotype was rescued when the AtUSR1 gene was transferred back to the mutant plants. Meanwhile, overexpression of AtUSR1 caused accelerated leaf senescence. Furthermore, the role of AtUSR1 in regulating leaf senescence is related to MYC2-mediuated jasmonic acid (JA) signaling pathway. MeJA treatments promoted the accumulation of AtUSR1 transcripts and this expression activation was dependent on the function of MYC2, a key transcription factor in JA signaling. Dual-luciferase assay results indicated that MYC2 promoted the expression of AtUSR1. Overexpression of AtUSR1 in myc2 mutant plants showed precocious senescence, while myc2 mutation alone caused a delay in leaf senescence, suggesting that AtUSR1 functions downstream to MYC2 in the JA signaling pathway in promoting leaf senescence.

Highlights

As a process of programmed cell death, leaf senescence is important in plants’ development and response to environmental stresses (Guo and Gan, 2005; Kim et al, 2018)
Different from the expression of SAG12that was not detected until the last stage of leaf senescence, the expression peak of AtUSR1 appeared at the early senescence stage
The results showed that leaves of the 35S::AtUSR1 lines displayed stronger while the usr1 mutant showed weaker Nitro-blue tetrazolium (NBT) staining compared with Col-0, suggesting that AtUSR1 rendered plant accumulating more reactive oxygen species (ROS) in leaves (Figure 5A)

Summary

Introduction

As a process of programmed cell death, leaf senescence is important in plants’ development and response to environmental stresses (Guo and Gan, 2005; Kim et al, 2018). In order to complete their life cycle, stressed plants often endeavor to reallocate nutrients to reproductive organs via the process of leaf senescence (Sedigheh et al, 2011). Leaf senescence can be induced by a large number of endogenous and environmental factors including age, plant hormones, light conditions, abiotic stresses, and pathogen infection. Significant changes in gene expression, metabolic, and physiological activities take place and the execution of leaf senescence eventually leads to programmed cell death (Quirino et al, 2000; KhannaChopra, 2012; Guo, 2013).

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Conclusion