ABF2, ABF3, and ABF4 Promote ABA-Mediated Chlorophyll Degradation and Leaf Senescence by Transcriptional Activation of Chlorophyll Catabolic Genes and Senescence-Associated Genes in Arabidopsis

Abstract

Chlorophyll (Chl) degradation is an integral process of leaf senescence, and NYE1/SGR1 has been demonstrated as a key regulator of Chl catabolism in diverse plant species. In this study, using yeast one-hybrid screening, we identified three abscisic acid (ABA)-responsive element (ABRE)-binding transcription factors, ABF2 (AREB1), ABF3, and ABF4 (AREB2), as the putative binding proteins of the NYE1 promoter. Through the transactivation analysis, electrophoretic mobility shift assay, and chromatin immunoprecipitation, we demonstrated that ABF2, ABF3, and ABF4 directly bound to and activated the NYE1 promoter in vitro and in vivo. ABA is a positive regulator of leaf senescence, and exogenously applied ABA can accelerate Chl degradation. The triple mutant of the ABFs, abf2abf3abf4, as well as two ABA-insensitive mutants, abi1-1 and snrk2.2/2.3/2.6, exhibited stay-green phenotypes after ABA treatment, along with decreased induction of NYE1 and NYE2 expression. In contrast, overexpression of ABF4 accelerated Chl degradation upon ABA treatment. Interestingly, ABF2/3/4 could also activate the expression of two Chl catabolic enzyme genes, PAO and NYC1, by directly binding to their promoters. In addition, abf2abf3abf4 exhibited a functional stay-green phenotype, and senescence-associated genes (SAGs), such as SAG29 (SWEET15), might be directly regulated by the ABFs. Taken together, our results suggest that ABF2, ABF3, and ABF4 likely act as key regulators in mediating ABA-triggered Chl degradation and leaf senescence in general in Arabidopsis.

BrWRKY65, a WRKY Transcription Factor, Is Involved in Regulating Three Leaf Senescence-Associated Genes in Chinese Flowering Cabbage

“…Consistent with its trend in our RNA-seq database, BrWRKY65 transcript level increased during senescence, reaching about 4.2- and 3.8-fold of the initial level at day seven and nine, respectively (Figure 4). In addition, as leaf yellowing is due to chlorophyll degradation [29,32,40,41,42,43], and dark-inducible ( DIN ) genes are induced in dark-adapted and senescing leaves [44,45], which have been used previously as markers to characterize senescence-associated responses. Therefore, we further searched the SAG genes in our RNA-seq transcriptome database, and three SAG s such as BrNYC1 (NON-YELLOW COLORING1/Chl b reductase) (XP_009139641.1) and BrSGR1 (STAY-GREEN1) (XP_018512704.1) associated with chlorophyll degradation, and BrDIN1 (XP_009150416.1) were selected.…”

“…Intriguingly, Arabidopsis ETHYLENE INSENSITIVE3 (EIN3) and ORE1/NAC2 establish a network controlling ethylene-induced leaf senescence via directly targeting NYE1 , NYC1 , and PAO [52]. More recently, abscisic acid (ABA)-responsive element (ABRE)-binding TFs ABF2, ABF3, and ABF4 from Arabidopsis are found to speed ABA-mediated chlorophyll degradation and leaf senescence by the trans-activation of NYE1 , NYE2 , NYC1 , PAO , SAG12 , and SAG29 [42]. Collectively, these results imply the existence of a complex regulatory network of chlorophyll degradation and leaf senescence involving multiple TFs.…”

Abscisic Acid Is a Major Regulator of Grape Berry Ripening Onset: New Insights into ABA Signaling Network

“…Interestingly, VvMYBA7, recently characterized as a regulator of the anthocyanins synthesis in vegetative organs, was up-regulated by ABA but only at the 20 h time-point, suggesting its direct induction by ABA, but not its participation to the ripening program (Matus et al, 2017). The role of ABA in down-regulating photosynthesis under stressful conditions, such as drought, salinity or low temperature, and during developmental processes, such as senescence (Lee et al, 2004; Yang et al, 2011; Gao et al, 2016), has been extensively described. It is not surprising then that at 44 h the functional enriched categories within the down-regulated genes involve different aspects of the photosynthetic metabolism.…”

Sensitivity of Pigment Content of Banana and Orchid Tissue Culture Exposed to Extremely Low Frequency Electromagnetic Fiel

“…More recent study found that chlorophyll degradation was also mediated by abscisic acid. Some genes that regulate the chlorophyll degradation in Arabidopsis had been described, including NYE1 and STAY GREEN genes (Gao et al 2016). Chlorophyll degradation is a crucial process during leaf senescence and fruit ripening because it helps plants to recycle nitrogen and other nutrients (Hortensteiner 2006).…”