Differential expression pattern of an acidic 9/13-lipoxygenase in flower opening and senescence and in leaf response to phloem feeders in the tea plant.
BACKGROUND
Lipoxygenase (LOXs) is a large family of plant enzymes that catalyse the hydroperoxidation of free polyunsaturated fatty acids into diverse biologically active compounds, collectively named phyto-oxylipins. Although multiple isoforms of LOXs have been identified in a wide range of annual herbaceous plants, the genes encoding these enzymes in perennial woody plants have not received as much attention. In Camellia sinensis (L.) O. Kuntze, no LOX gene of any type has been isolated, and its possible role in tea plant development, senescence, and defence reaction remains unknown. The present study describes the isolation, characterization, and expression of the first tea plant LOX isoform, namely CsLOX1, and seeks to clarify the pattern of its expression in the plant's defence response as well as in flower opening and senescence.


RESULTS
Based on amino acid sequence similarity to plant LOXs, a LOX was identified in tea plant and named CsLOX1, which encodes a polypeptide comprising 861 amino acids and has a molecular mass of 97.8 kDa. Heterologous expression in yeast analysis showed that CsLOX1 protein conferred a dual positional specificity since it released both C-9 and C-13 oxidized products in equal proportion and hence was named 9/13-CsLOX1. The purified recombinant CsLOX1 protein exhibited optimum catalytic activity at pH 3.6 and 25°C. Real-time quantitative PCR analysis showed that CsLOX1 transcripts were detected predominantly in flowers, up-regulated during petal senescence, and down-regulated during flower bud opening. In leaves, the gene was up-regulated following injury or when treated with methyl jasmonate (MeJA), but salicylic acid (SA) did not induce such response. The gene was also rapidly and highly induced following feeding by the tea green leafhopper Empoasca vitis, whereas feeding by the tea aphid Toxoptera aurantii resulted in a pattern of alternating induction and suppression.


CONCLUSIONS
Analysis of the isolation and expression of the LOX gene in tea plant indicates that the acidic CsLOX1 together with its primary and end products plays an important role in regulating cell death related to flower senescence and the JA-related defensive reaction of the plant to phloem-feeders.
Liu
Shouan
S
Tea Research Institute of Chinese Academy of Agricultural Sciences, Hangzhou, 310008, China.
Han
Baoyu
B
D000595:Amino Acid Sequence; D000818:Animals; D001042:Aphids / Q000502:physiology; D001483:Base Sequence; D028241:Camellia sinensis / Q000201:enzymology / Q000235:genetics* / Q000469:parasitology; D004591:Electrophoresis, Polyacrylamide Gel; D035264:Flowers / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006430:Hemiptera / Q000502:physiology; D006790:Host-Parasite Interactions; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D019787:Linoleic Acid / Q000378:metabolism; D008084:Lipoxygenase / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D052585:Phloem / Q000201:enzymology / Q000235:genetics / Q000469:parasitology; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000494:pharmacology; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics* / Q000469:parasitology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013314:Stress, Mechanical; D013379:Substrate Specificity
D010937:Plant Growth Regulators; D010940:Plant Proteins; D019787:Linoleic Acid; C117433:13-lipoxygenase; D008084:Lipoxygenase