Abstract
The ethylene response factor (ERF) and phytohormone jasmonate (JA) are reported to function in leaf senescence. The involvement of ERF in JA-mediated leaf senescence, however, needs to be elucidated. In the present work, we demonstrate a Chinese flowering cabbage ERF transcription factor (TF), BrERF72, that is associated with JA-promoted leaf senescence. Exogenous application of methyl jasmonate (MeJA)-accelerated leaf senescence of Chinese flowering cabbage, evidenced by the data that MeJA treatment led to the stronger reduction in the maximum quantum yield (Fv/Fm), photosynthetic electron transport rate (ETR), and total chlorophyll content, while significant induction in the expression of several senescence-associated genes (SAGs) including BrSAG12, BrSAG19, and chlorophyll catabolic genes (CCGs) BrPAO1, BrNYC1, BrPPH1, and BrSGR1. Increases in levels of endogenous JA and transcripts of JA biosynthetic genes BrLOX4, BrAOC3, and BrOPR3 were also found after MeJA treatment. BrERF72 was a MeJA-inducible, nucleus-localized protein, and possessed trans-activation ability. Transient overexpression of BrERF72 in tobacco leaves also promoted leaf senescence. More importantly, further experiments revealed that BrERF72 directly activated expression of BrLOX4, BrAOC3, and BrOPR3 through binding to their promoters via the GCC or DRE/CRT cis-element. Together, the novel JA-ERF association reported in our study uncovers a new insight into the transcriptional regulation of JA production mediated by ERF during JA-promoted leaf senescence in Chinese flowering cabbage.
Highlights
As the final phase of development, leaf senescence is considered as an important biological process in plants that nutrition substances in senescing leaves were reallocated to the newly formed organs, which can maximize plants viability in the year[1,2,3]
We compared the expression of senescence-associated genes (SAGs) including BrSAG12, BrSAG19, and chlorophyll catabolic genes (CCGs) such as BrPAO1, BrNYC1, BrPPH1, and BrSGR1 encoding pheophorbide a oxygenase (PAO), NON-YELLOW COLORING (NYC), pheophytin pheophorbide hydrolase (PPH), and STAYGREEN (SGR), respectively, between methyl jasmonate (MeJA)-treated and control leaves
MeJA treatment obviously increased the transcripts of those genes compared to control, with a 1.18, 1.67, 1.29, 1.48, and 1.41-fold induction for BrSAG12, BrSAG19, BrNYC1, BrPPH1, and BrSGR1 at 7 days, and a 1.21-fold induction for BrPAO1 at 5 days of storage, respectively (Fig. 1c)
Summary
As the final phase of development, leaf senescence is considered as an important biological process in plants that nutrition substances in senescing leaves were reallocated to the newly formed organs, which can maximize plants viability in the year[1,2,3]. The initiation and development of leaf senescence is tightly controlled by various endogenous and environmental factors, such as developmental stage, phytohormones, nutrients, and stresses[2,8,9]. Exogenously applied JA or its bioactive derivatives methyl jasmonate (MeJA) stimulate leaf senescence in several plants such as Arabidopsis[11,12,13,14], wormwood[15], barley[16], maize[17], and rice[18], by upregulating some senescence-associated genes (SAGs). JA is an important factor in inducing leaf senescence 10,19
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