Plant basal resistance - Universiteit Utrecht

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Chapter 3 IGL-derived BXs. It is possible that IGL has a more prominent contribution during the later stages of the interaction, when more IGL-derived indole is channelled into the BX pathway and replenishes the rapidly declining pool of DIMBOA-glc. The extent of this contribution requires further investigation and can be addressed by comparing BX profiles between indole-producing Igl lines and indole-deficient igl lines at different stages of the plant- parasite interaction. These lines will also prove useful to assess the role of IGL-dependent indole emission in tritrophic interactions and indirect defence against herbivores. Early-acting post-invasive plant defence is marked by a rapid accumulation of reactive oxygen species followed by deposition of callose-rich papillae (Ton et al., 2009; Luna et al., 2011). Our finding that bx1 mutant lines are affected in PAMP-induced callose suggests a regulatory function of BXs in this defence response (Figure 7). Recently, it was reported that DIMBOA acts as an electron acceptor for apoplastic cytokinin dehydrogenase, thereby contributing to the degradation of cytokinins (Frebortova et al., 2010). Since cytokinins can antagonise abscisic acid (ABA)-regulated plant processes (Shkolnik-Inbar and Bar-Zvi, 2010; Subbiah and Reddy, 2010; Vysotskaya et al., 2010), it is tempting to speculate that DIMBOA-catalysed cytokinin degradation contributes to ABA-dependent priming of callose deposition (Ton et al., 2009). In support of this, we found that apoplast infiltration with DIMBOA boosts callose deposition (Figure 8). Interestingly, Frebortova et al. (2010) proposed that DIMBOA-dependent degradation of cytokinins depends on the –N-OH group of DIMBOA at the indolic ring, which is absent in HDMBOA after O-methylation. Indeed, HDMBOA-glc failed to elicit callose deposition in our experiments (Figure 8). Future research will be necessary to decipher the interplay between extracellular DIMBOA, cytokinins and ABA in the regulation of post-invasive cereal defence against pests and diseases. PAMP-induced callose in Arabidopsis requires intact biosynthesis of the 4-methylated indolic GS 4MI3G and subsequent hydrolysis by the atypical myrosinase PEN2 (Clay et al., 2009). This discovery revealed an important regulatory function of breakdown products of indolic glucosinolates in Arabidopsis innate immunity, but at the same time raised the question how non-Brassicaceous plants regulate callose deposition. In this study, we have examined whether BXs fulfil a similar regulatory function in maize, and found that BX-deficient bx1 lines are indeed dramatically reduced in their capacity to deposit PAMP- induced callose compared to BX-producing Bx1 lines (Figure 7). Moreover, of the two chitosan-inducible BXs, only DIMBOA elicited callose deposition upon infiltration into the apoplast, whereas infiltration with similar amounts of HDMBOA-glc failed to trigger callose depositions (Figure 8). A similar compound-specificity was found for the transcriptional feed-back regulation of the BX pathway (Figure 6). Since DIMBOA and HDMBOA-glc are both degraded into MBOA and BOA (Maresh et al., 2006; Macias et al., 2007), it can be concluded that extracellular DIMBOA, rather than its successive break-down products, is responsible for the regulation of callose deposition and Bx gene expression (Figure 9). We, therefore, 78
79 Role of benzoxazinoids in maize immunity hypothesize that this signalling function originates from a conserved detoxification response, which prevents auto-toxic build-up of BXs by translocation to the apoplast. Once deposited into the apoplast, BX-glucosides become hydrolysed and captured in a matrix of callose to provide targeted chemical defence against invading parasites. The striking analogy with indolic GS metabolites in Arabidopsis points to a conserved regulatory function of indole- derived secondary metabolites in innate immunity across the plant kingdom. CONCLUSION BX-deficient maize is more susceptible to aphids and is affected in penetration <strong>resistance</strong> against fungal pathogens. The difference in <strong>resistance</strong> between BX-deficient and BX- producing maize lines occurs before the onset of major tissue damage and manifests itself as increased accumulation of BX compounds in the apoplast. In addition to its contribution as a biocidal defence metabolite, extracellular DIMBOA regulates Bx gene expression and PAMP-induced callose, which reveals a novel regulatory function of BX metabolites in cereal innate immunity against pests and diseases. ACKNOWLEDGEMENTS The work described in this manuscript was supported by a BBSRC Institute Career Path Fellowship (no. BB/E023959/1) to Jurriaan Ton. We thank Ted Turlings for critically proofreading an earlier version of this manuscript. We also thank the technical support of the SCIC of Universitat Jaume I and Cristian Barrera for assistance during NMR analysis.
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Plant basal resistance: genetics, b
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Most of the research described in t
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Promotor: Prof. dr. Ir. C.M.J. Piet
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10 CHAPTER 1 General Introduction A
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Chapter 1 (PRRs; Gomez-Gomez and Bo
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Chapter 1 by avirulent pathogens (R
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Chapter 1 Selective non-pathogenic
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Chapter 1 an endogenous plant signa
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Chapter 1 between defence signallin
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Chapter 1 rarely provides complete
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Chapter 1 genetic resources for Ara
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Chapter 1 metabolites are biosynthe
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Page 30: Chapter 1 latest insights. This Cha
Page 33 and 34: ABSTRACT 33 Genetic dissection of b
Page 35 and 36: 35 Genetic dissection of basal defe
Page 45 and 46: Natural variation in responsiveness
Page 57: 57 Genetic dissection of basal defe
Page 61 and 62: ABSTRACT 61 Role of benzoxazinoids
Page 63 and 64: 63 Role of benzoxazinoids in maize
Page 67 and 68: Chemical treatments and callose qua
Page 69 and 70: Aphid infestation stimulates apopla
Page 77: 77 Role of benzoxazinoids in maize
Page 81 and 82: Table S1: Primers used for RT-qPCR
Page 86 and 87: 86 CHAPTER 4 Benzoxazinoids in root
Page 88 and 89: Chapter 4 INTRODUCTION Plants have
Page 90 and 91: Chapter 4 Our study presents eviden
Page 92 and 93: Chapter 4 Maize - P. putida FBC004
Page 94 and 95: Chapter 4 P. putida is tolerant to
Page 96 and 97: Chapter 4 Impact of DIMBOA on the P
Page 98 and 99: Chapter 4 PP5286 dut deoxyuridine 5
Page 100 and 101: Chapter 4 DIMBOA-producing wild-typ
Page 102 and 103: Chapter 4 DISCUSSION The rhizospher
Page 104 and 105: Chapter 4 patterns, we considered t
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Page 108 and 109: 108 CHAPTER 5 General Discussion
Page 110 and 111: Chapter 5 QTL was caused by a polym
Page 112 and 113: Chapter 5 Figure 1: CYP81D11 regula
Page 114 and 115: Chapter 5 et al., 2009), and allele
Page 116 and 117: Chapter 5 defence against different
Page 118 and 119: Chapter 5 occurred at time-points l
Page 120 and 121: Chapter 5 rhizospheric signals that
Page 122 and 123: Chapter 5 glucosinolate profiles. 1
Page 124 and 125: References References Abramovitch R
Page 126 and 127: References QTL mapping and characte
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References Gianoli E, Niemeyer HM (
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References Kliebenstein DJ, Kroyman
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References Studies in Natural Produ
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References Geniostoma antherotrichu
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References Todesco M, Balasubramani
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References Walters DR, Paterson L,
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Summary Summary Basal resistance in
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Samenvatting Samenvatting Basale re
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Samenvatting inzichten opgeleverd i
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Acknowledgments Acknowledgements In
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Curriculum vitae Shakoor was born o
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List of Publications Published arti
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