Ethylene-Induced Flavonol Accumulation in Guard Cells Suppresses Reactive Oxygen Species and Moderates Stomatal Aperture

Wake Forest University, Winston-Salem, North Carolina, United States
Plant physiology (Impact Factor: 6.84). 03/2014; 164(4). DOI: 10.1104/pp.113.233528
Source: PubMed


Guard cell swelling controls the aperture of stomata, pores that facilitate gas exchange and water loss from leaves. The hormone abscisic acid (ABA) has a central role in regulation of stomatal closure through synthesis of second messengers, which include reactive oxygen species (ROS). ROS accumulation must be minimized by antioxidants to keep concentrations from reaching damaging levels within the cell. Flavonols are plant metabolites that have been implicated as antioxidants; however, their antioxidant activity in planta has been debated. Flavonols accumulate in guard cells of Arabidopsis thaliana, but not surrounding pavement cells, as visualized with a flavonol-specific dye. The expression of a reporter driven by the promoter of CHALCONE SYNTHASE (CHS), a gene encoding a flavonol biosynthetic enzyme, in guard cells, but not pavement cells, suggests guard cell specific flavonoid synthesis. Increased levels of ROS were detected using a fluorescent ROS sensor in guard cells of tt4-2, which has a null mutation in CHS and therefore synthesizes no flavonol antioxidants. Guard cells of tt4-2 show more rapid ABA-induced closure than wild-type, suggesting flavonols may dampen the ABA-dependent ROS burst that drives stomatal closing. The levels of flavonols are positively regulated in guard cells by ethylene treatment in wild-type, but not in the ethylene-insensitive2-5 (ein2-5) mutant. Additionally, in both ethylene-overproducing1 (eto1) and ethylene-treated wild-type plants, elevated flavonols lead to decreasing ROS and slower ABA-mediated stomatal closure. These results are consistent with flavonols suppressing ROS accumulation and decreasing the rate of ABA-dependent stomatal closure, with ethylene-induced increases in guard cell flavonols modulating these responses.

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Available from: Gloria K Muday, Oct 19, 2014
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    • "Anotherfunctionrecentlyhighlightedforflavonoidsistheirrole asantioxidants,havingrolesinstomatalclosureanddrought response(Nakabayashietal.,2014;Watkinsetal.,2014).Itseems possiblethatthesecompoundscouldservetohelpbufferagainst damagefromROSgeneratedincellsundergoinginfection. TwoVestitoneReductasegenesneededfortheproductionof medicarpin,oneofwhichisexpressedatinfectionsitesin theepidermis(Breakspearetal.,2014),werealsofoundtobe "
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    ABSTRACT: Genome-wide expression studies on nodulation have varied in their scale from entire root systems to dissected nodules or root sections containing nodule primordia (NP). More recently efforts have focused on developing methods for isolation of root hairs from infected plants and the application of laser-capture microdissection technology to nodules. Here we analyze two published data sets to identify a core set of infection genes that are expressed in the nodule and in root hairs during infection. Among the genes identified were those encoding phenylpropanoid biosynthesis enzymes including Chalcone-O-Methyltransferase which is required for the production of the potent Nod gene inducer 4',4-dihydroxy-2-methoxychalcone. A promoter-GUS analysis in transgenic hairy roots for two genes encoding Chalcone-O-Methyltransferase isoforms revealed their expression in rhizobially infected root hairs and the nodule infection zone but not in the nitrogen fixation zone. We also describe a group of Rhizobially Induced Peroxidases whose expression overlaps with the production of superoxide in rhizobially infected root hairs and in nodules and roots. Finally, we identify a cohort of co-regulated transcription factors as candidate regulators of these processes.
    Frontiers in Plant Science 08/2015; 6:575. DOI:10.3389/fpls.2015.00575 · 3.95 Impact Factor
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    • "Recently quercetin derivatives in stomata guard cells have been shown to reduce the level of H 2 O 2 , which is an intermediate in the ABA signalling, thus antagonizing ABA-induced stomata closure (Watkins et al., 2014). This observation conforms to the notion NO and ROS are downstream components of the ABA signalling network (Tossi et al., 2012). "
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    • "The actions of antioxidant enzymes may need to be complemented by those of other ROS scavenging systems during severe stress conditions (Apel and Hirt 2004). Flavonoids served as antioxidants in response to different stresses, such as heavy metal, drought, and salt (Izbianska et al. 2014; Tattini et al. 2004; Watkins et al. 2014). It mainly consists of anthocyanins, flavonols, flavanols, and proanthocyanidins (PAs) or condensed tannins (Debeaujon et al. 2001). "
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    ABSTRACT: Key message EaCHS1 functions in the tolerance of plantlets to salinity stress by maintaining ROS homeostasis. Abstract Chalcone synthase (CHS) is an essential enzyme in the biosynthesis of flavonoids. Expression of CHS is governed by a wide range of environmental stimuli, including UV light, pathogen attack, and circadian clocks. However, little research exists on the relationship between CHS and salinity stress. In this work, we constructed separate overexpression and RNA interference vectors of EaCHS1, and transferred them into tobacco. Overexpression of EaCHS1 increased the production of downstream flavonoids and the expressions of related genes in the phenylpropanoid pathway. It also improved resistance to salinity stress during seed germination and root development. In contrast, heterologous silencing of endogenous CHS in tobacco by a conserved EaCHS1 fragment had opposite effect. Together, our results indicated that changing the expression level of EaCHS1 in plants alters the accumulation of flavonoids and regulates plantlet tolerance to salinity stress by maintaining ROS homeostasis.
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