title: A NAP-AAO3 regulatory module promotes chlorophyll degradation via ABA biosynthesis in Arabidopsis leaves.
abstract: Chlorophyll degradation is an important part of leaf senescence, but the underlying regulatory mechanisms are largely unknown. Excised leaves of an Arabidopsis thaliana NAC-LIKE, ACTIVATED BY AP3/PI (NAP) transcription factor mutant (nap) exhibited lower transcript levels of known chlorophyll degradation genes, STAY-GREEN1 (SGR1), NON-YELLOW COLORING1 (NYC1), PHEOPHYTINASE (PPH), and PHEIDE a OXYGENASE (PaO), and higher chlorophyll retention than the wild type during dark-induced senescence. Transcriptome coexpression analysis revealed that abscisic acid (ABA) metabolism/signaling genes were disproportionately represented among those positively correlated with NAP expression. ABA levels were abnormally low in nap leaves during extended darkness. The ABA biosynthetic genes 9-CIS-EPOXYCAROTENOID DIOXYGENASE2, ABA DEFICIENT3, and ABSCISIC ALDEHYDE OXIDASE3 (AAO3) exhibited abnormally low transcript levels in dark-treated nap leaves. NAP transactivated the promoter of AAO3 in mesophyll cell protoplasts, and electrophoretic mobility shift assays showed that NAP can bind directly to a segment (-196 to -162 relative to the ATG start codon) of the AAO3 promoter. Exogenous application of ABA increased the transcript levels of SGR1, NYC1, PPH, and PaO and suppressed the stay-green phenotype of nap leaves during extended darkness. Overexpression of AAO3 in nap leaves also suppressed the stay-green phenotype under extended darkness. Collectively, the results show that NAP promotes chlorophyll degradation by enhancing transcription of AAO3, which leads to increased levels of the senescence-inducing hormone ABA.
authors.affiliation: Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401 BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831.
authors.forename: Jiading
authors.initials: J
authors.lastname: Yang
authors.affiliation: Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401 BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831.
authors.forename: Eric
authors.initials: E
authors.lastname: Worley
authors.affiliation: Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401 BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 mudvardi@noble.org.
authors.forename: Michael
authors.identifier: http://orcid.org/0000-0001-9850-0828
authors.initials: M
authors.lastname: Udvardi
mesh_terms: D000040:Abscisic Acid / Q000096:biosynthesis* / Q000494:pharmacology; D042931:Aldehyde Oxidase / Q000235:genetics* / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D016922:Cellular Senescence / Q000235:genetics; D002734:Chlorophyll / Q000378:metabolism*; D003624:Darkness; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D010641:Phenotype; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C110811:NAP protein, Arabidopsis; D012333:RNA, Messenger; D002734:Chlorophyll; D000040:Abscisic Acid; C470342:AAO3 protein, Arabidopsis; D042931:Aldehyde Oxidase