Pertinently, jasmonates and salicylic acid have been emerging as novel growth regulators known to retort and provide immunity to plant organs against environmental stresses like senescence. Oxidative stress is hypothesized as hallmark for instigation of floral senescence in ethylene insensitive species. Taken together, these results indicate that TgNAP enhances SA biosynthesis and ROS accumulation to positively regulate petal senescence in tulip. Meanwhile, TgNAP repressed ROS scavenging by directly inhibiting PEROXIDASE 12 (POD12) and POD17 expression. Further evidence indicated that TgNAP activates the transcriptions of two key SA biosynthetic genes ISOCHORISMATE SYNTHASE 1 (TgICS1) and PHENYLALANINE AMMONIA-LYASE 1 (TgPAL1)) through directly binding to their promoter regions. Additionally, inhibition of SA biosynthesis prolonged the lifespan of TgNAP-silenced petal discs. Silencing of TgNAP by VIGS assay delayed SA and H2O2-induced petal senescence in tulip, whereas overexpression of TgNAP promoted the senescence process in Arabidopsis (Arabidopsis thaliana) plants. TgNAP was up-regulated in senescing petals of tulip while exogenous SA and H2O2 treatments substantially promoted petal senescence in tulip. In this study, tulip TgNAP (NAC-like, activated by APETALA3/PISTILLATA), was characterized as positively regulating tulip petal senescence through dually regulating SA biosynthesis and ROS detoxification pathways. Salicylic acid (SA) and reactive oxygen species (ROS) are two prominent factors involved in plant senescence regulation. Petal senescence is a crucial determinant for ornamental quality and economic value of floral crops. Taken together, this study provides evidences to certify ethylene roles and TgACS functions during flower senescence in tulip. Transient down-regulation of TgACS by VIGS assay in tulip petals delayed senescence, while over-expressed TgACS1 in tobacco promoted leaf senescence.
Exogenous treatment of cutting flowers with 1-MCP or ethephon resulted in delayed or enhanced petal senescence, respectively. Moreover, ethylene production was stimulated as evidenced by increasing in ACS activity and ethylene biosynthesis-related genes expression. Additionally, senescence-associated genes were identified and significantly up-regulated, coupled with increased ROS contents, rapid water loss and accelerated cell membrane breakdown.
Primary metabolites profiling revealed that sugars, amino acids and organic acids preferentially accumulated in senescent petals. In this study, we characterized the physiological indexes in the process of petal senescence, as well as metabolic and ethylene responses in tulip cultivar 'American Dream', and further identified the role of ethylene biosynthesis genes TgACS by transgenic and transient assays. However, the manner of petal senescence in tulip is still less defined.
Flower senescence is classified into ethylene-dependent and ethylene-independent manners and determines the flower longevity which is valuable for ornamental plants.
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