NABIL KILLINY ASSISTANT PROFESSOR PLANT PATHOLOGY UNIVERSITY OF FLORIDA. Citrus responses to huanglongbing

Transcription

1 NABIL KILLINY ASSISTANT PROFESSOR PLANT PATHOLOGY UNIVERSITY OF FLORIDA Citrus responses to huanglongbing

2 HLB is Vector-borne Disease! Vector psyllids Pathogen Ca. Liberibacter asiaticus. Host Citrus spp. and relatives

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4 I- Leaf pigments

5 Chlorophylls The chlorophylls are the most abundant pigments in higher plants Chlorophylls play a key role in photosynthesis by harvesting the sunlight energy and transferring the electrons to the other molecules in the reaction center In addition, chlorophyll derivatives, such as chlorophyllide, was found to be formed after herbivory or when chlorophyllase was freed from the ER by cell disruption Chl a Chl b

6 Carotenoids Carotenoids are a large group of tetraterpenoids, divided into two classes. Carotenes (No O 2 ) and xanthophylls (O 2 ) In higher plants, carotenoids play an important role in the variegation of leaves, flowers, fruits, serve as precursors for many biologically important compounds such as vitamin A, and can also act as antioxidants Carotenoids protect chlorophylls from photodamage

7 In HLB pathosystem HLB-symptoms involve chlorosis and/or discoloration due to the degradation of photosynthetic pigments such as chlorophylls and carotenoids. Recently, our recognition of physiological events associated with CLas-infection and/or D. citri-infestation has been greatly improved. However, the mechanisms of HLB-symptom development are still unexplored.

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9 Infection with CLas increases zeaxanthin Infestation with D. citri increases chlorophyllide a

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12 CLas and D. citri alter the expression of genes implicated in carotenoids and chlorophylls biosynthesis pathways.

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14 Conclusion The pigment-dependent defense system varys based on the stressor type (CLas, D. citri, or both together). CLas increases zeaxanthin and decreases other pigments, whereas, D. citri increases chlorophyllide a and decreases other pigments. As results of that, both Clas and D. citri produce similar symptoms. Accumulation of ABA in the presence of CLas

15 II- Carboxylic compounds

16 Overall, 36 compounds were detected in citrus leaf extract using GC-MS 19 amino acids 3 NP amino acids 9 organic acids 5 fatty acids compounds Concentration (mean±standard deviation) z Control CLas-infected D. citri-infested Double-attacked Amino acids Non-proteinogenic amino acids γ-aminobutyric acid 1262±656 c 3685±599 b 5809±821 a 4697±1181 b L-Pyroglutamic acid 405±23 a 284±31 bc 301±41 b 252±25 c Tyramine 950±73 a 416 ±270 b 869±130 a 773±193 a Basic amino acids L-Histidine 2453±100 ns 2315±233 ns 2356±216 ns 2350±135 ns L-Lysine 195±13 a 96 ±33 b 105±27 b 130±30 b Acidic amino acids L-Aspartic acid 814±331 ns 642±136 ns 588±304 ns 365±158 ns L-Glutamic acid 3493±701 a 1268±276 b 2681±215 a 704±140 b Polar side amino acids L-Asparagine 10490±1095 a 8312±991 ab 5909±2987 b 8284±1615 ab L-Cysteine 24±5 ns 49±16.68 ns 40±18 ns 27±3 ns L-Glutamine 5442±2758 a 4014±1763 b 4821±1237 b 2299±399 b L-Serine 3215±1429 b 6642±1679 a 2799±1974 ab 2698±1275 ab L-Threonine 134±101 b 188±50 a 149±67 a 168±17 a L-Tyrosine 354±57 ns 352±163 ns 310±144 ns 387±35 ns Non-polar side amino acids L-Alanine 700±106 b 949±155 ab 704±248 b 1251±245 a Glycine 27±4 b 63±11 a 39±14 b 38±9 b L-Isoleucine 67±12 b 173±60 a 106±36 ab 158±39 a L-Leucine 65±6 ns 60±6 ns 63±4 ns 59±4 ns L-Methionine 219±57 a 183±26 b 150±64 b 190±33 b L-Phenylalanine 361±88 b 465±46 a 186±73 b 475±57 a L-Proline 16910±2846 c 34549±2654 a 26230±3606 b 27915±3788 b L-Tryptophan 47±26 b 222±80 a 206±111 a 210±55 a L-Valine 152±55 ns 158±72 ns 121±59 ns 164±62 ns Total amino acids 47779±4711 c 65084±2985 a 54540±3254 b 53598±3844 b Organic acids Mono-carboxylic organic acids Benzoic acid 2539±438 b 5344±739 a 2433±147 b 4444±334 a Ferulic acid 4607±755 a 1928±421 b 984±283 c 1729±461 ab t-jasmonic acid 242±11 c 297±17 c 432±16 a 356±23 b Quinic acid 1776±445 b 715±226 c 2401±411 a 633±184 c Salicylic acid 915±74 b 2521±646 a 1363±298 b 2345±485 a Di-carboxylic organic acids Fumaric acid 4001±246 b 6740±733 ab 9119±642 a 7302±298 a Malic acid 39713±8163 a 17937±4439 b 33373±6071 ab 20741±4711 ab Succinic acid 7619±340 c 17431±3327 ab 11486±2991 bc 19465±3830 a Tri-carboxylic organic acids Citric acid 3859±396 b 9574±715 a 7130±395 a 7809±255 a Total organic acids 65272±2214 ns 62487±8620 ns 68721±7378 ns 64825±9420 ns Fatty acids Linoleic acid (C18:2) Stearic acid (C18:0) 1433±195 c 62±14 c 2169±237 b 202±42 ab 3194±250 a 312±83 a 2418±235 b 185±93 b α-linolenic acid (C18:3) Total fatty acids 560±62 d 5281±174 c 830±102 c 7440±169 b 1615±110 a 10461±325 a 1162±107 b 7366±210 b Oleic acid (C18:1) 1288±216 b 1936±377 a 2422±322 a 1104±174 b Palmitic acid (C16:0) 1937±5 d 2303±59 c 2919±61 a 2496±85 b 16 11/2/2017

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18 AA OA FA

19 The principal components analysis (PCA) showed a clear separation between the CLas-infected and double-attacked plants (as a group) and both control and D. citri-infested plants

20 The gene expression of all involved genes in JA pathway were upregulated in D. citri-infested plants compared to control (up to 6.5 folds)

21 Phenylalanine ammonia-lyase and isochorismate synthase, which are involved in SA-biosynthesis, and proline dehydrogenase 1and δ-1-pyrroline-5- carboxylate dehydrogenase 12A1, genes implicated in glutamine and proline metabolism were highly expressed in CLas-infected plants.

22 Conclusion Multiple signaling carboxy-molecules are involved in citrus response to CLas-infection and/or D. citri-infestation through three major pathways; I) Induction of SA-mediated pathway, which is associated with defense response for biotrophic pathogens II) Induction of JA-mediated pathway, which is associated with defense against insects herbivory such as D. citri. III) Induction of glutamine-proline pathway, which is implicated in ROS generation due to the activity of ProDH and P5CDH

23 II- Phytohormones Multiple phytohormonal signaling mediates citrus responses to Candidatus Liberibacter asiaticus and its vector Diaphorina citri. Accepted in physiological and molecular plant pathology

24 Phytohormones are An organic substance have a several structural have a different chemical properties. Produced naturally in plant cells functioning at various sites At low concentration in complex matrix Regulate plant development and growth signaling networks and most physiological functions, from formation, germination and development to adaption to biotic and abiotic stress Divided into many classes (groups) on basis of chemical structures and physiological function

25 Phytohormones classes In the past Currently Auxins Cytokinins Gibberellins Abscisic acid (ABA) Ethylene (ET) Salicylates (SAs) Jasmonates (JAs) Brassinosteroids (BRs) Peptide hormones (PHs) Strigolactones (STRs)

26 Phytohormones roles In the past ( SAs JAs ABA ET GAs CKs AUXs BRs PHs STRs Transcriptional regulation Stress associated phytohormones Growth associated phytohormones

27 Phytohormones roles Biotic/Abiotic Stress Currently SAs JAs ABA ET GAs CKs AUXs BRs PHs STRs Defense gene expression Defense Response

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29 Both CLas and D. citri induce the auxins levels in citrus leaves.

30 Both CLas and D. citri induce the auxins precursor level in citrus leaves.

31 Salicylic acid is associated with citrus defense response for CLas infection.

32 Both CLas and D. citri induce the SAs precursor level in citrus leaves.

33 Infection with CLas and infestation with D. citri increased ABA and its precursor levels in citrus leaves.

34 The infestation with D. citri increased tja and its precursor levels in citrus leaves. The octadecanoid pathway

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36 PCA reveals contrasting phytohormonal-defense mechanisms against CLas and D. citri /2/2017

37 Summary Double-attacked CLas-infection D. citri-infestation Phenylalanine Tryptophan Zeaxanthin Linolenic acid SAs (BA, CA, and SA) AUXINS (IAA, IBA, and IPA) ABA tja SA-mediated pathway JA/ET-mediated pathway 11/2/2017