A positive feedback regulatory loop, SA-AtNAP-SAG202/SARD1-ICS1-SA, regulates salicylic acid biosynthesis and leaf senescence in Arabidopsis
Salicylic acid (SA) is an important plant hormone that plays critical roles in plant defense and leaf senescence. SARD1, a transcription factor (TF), directly regulates isochorismate synthase 1 (ICS1) and SA biosynthesis in defense response. The upstream TF regulating SARD1 and the regulatory mechanism of SA biosynthesis during leaf senescence are unknown. Here we report that AtNAP, a senescence-specific NAC family TF, directly regulates a senescence-associated gene named SAG202 (previously reported as SARD1). SAG202/SARD1 and ICS1 are upregulated during leaf senescence, and are co-induced with inducible overexpression of AtNAP. The induction of these genes leads to high levels of SA and precocious senescence in leaves. Individual knockout mutants of sag202/sard1 and ics1 have markedly reduced SA levels and display a significantly delayed leaf senescence phenotype. Furthermore, SA positively feedback regulates AtNAP and SAG202/SARD1. This research reveals a unique regulatory loop of SAAtNAP-SAG202/SARD1-ICS1-SA in SA biosynthesis during leaf senescence in Arabidopsis. It also provides further evidence for a critical role of SA in controlling leaf longevity.
Watkins, Christopher; Giovannoni, James
M.S., Horticultural Biology
Master of Science
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