Response of γ-Aminobutyric Acid Metabolic Pathway in Tea Plants to Early Infestation of Ectropis obliqua
Tea geometrid(Ectropis obliqpua Prout)infestation induces tea plants to release massive amounts of volatile organic compounds(VOCs),which are widely reported as important chemical cues that either repel the pests or attract their enemies.However,the spatial variations and the roles of the non-volatile metabolites in tea leaves infested by the tea geometrids are confusing.Taking tea leaves as materials,the feeding of E.obliqua was limited at the leaf tip,and then the tissues at the leaf tip,middle and base were collected.The non-volatile metabolites of the tissues at the three sites were identified and analyzed by ultra-high performance liquid chromatography-quadrupole orbitrap mass spectrometry(UHPLC-Q-Exactive/MS).The results demonstrate that compared with the blank control and mechanical injury tea leaves,tea geometrids induced 11 differential metabolites,including six dimeric catechins,three amino acids(including y-aminobutyric acid),one flavonoid and flavonoid glycoside,and one phenolic acid compound.After the infestation of the tea geometrids,the relative contents of y-aminobutyric acid at the three sites in tea leaves were significantly increased compared to the blank control tea leaves,and increased by 1.99-fold in the middle and base of leaves.In addition,the key genes involved in the y-aminobutyric acid biosynthetic pathway were upregulated at all three sites of tea leaves.There was a significant positive correlation between the relative content of y-aminobutyric acid and the relative content of glutamic acid(P＜0.05).When the tea geometrids were fed with artificial diet supplemented with 0.2 mg·g-1,0.5 mg·g-1 and 2.0 mg·g-1 y-aminobutyric acid,their body weight and length were both significantly decreased compared with the control(P＜0.05).The present study indicates that the inhibitory neurotransmitter y-aminobutyric acid plays a pivotal role in the early defense response against tea geometrids,which will shed light on the biochemical resistance mechanism of the tea plants.
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