Molecular Mechanism Of (Z)-3-hexenol-induced Defense Induced In Tea Plant Against Ectropis Obliqua Prout

As a result,plants have developed a massive reprogramming of metabolic pathways and formed induced defense mechanisms to defend themselves.To be more efficient in countering such situations,plants make use of their“defense priming”mechanisms for pre-emptive activation of defense-related genes and pathways.Green leaf volatiles?GLVs?play a vital role in priming herbivore-associated defense responses;they accelerate and/or enhance the reaction of plants when attacked.However,much less is known about how priming agents precisely regulate subsequent responses.The tea plant Camellia sinensis?L.?,which originated in China,is an economically important evergreen horticultural crop rich in beneficial metabolites,such as tea polyphenols,theanine,and polysaccharides.However,tea plants heavily suffer from the tea geometrid?TG?Ectropis obliqua Prout,which are chewing insect pests of tea bushes in China.In tea plants,?Z?-3-hexenol?z3HOL?,an important component of GLVs,can effectively prime the defense of tea against tea geometrids.In this study,we use z3HOL to spray Longjing 43 tea seedlings and take their young leaves to feed the caterpillars,then to determine the growth and development of the caterpillars in different treatments.We employed RNA-sequencing to survey the differentially expressed genes,at the transcriptional level,of the TG-infested tea plants with or without primed by z3HOL.The expression level of differentially expressed genes was performed based on Quantitative real-time PCR.The main results are as follows:?1?Feeding of tea leaves continuously treated by z3HOL could significantly reduce the average weights of the second and third instar larvae were 1.3-and 1.25-fold higher than reared on the control plants,but had no obvious effect on the 4th instar larvae.The death rates of second and third instar larvae of TG fed on z3HOL-treated tea plants were significantly higher than those fed on control plants.However,compared with the control,the masses and death rates of the fourth instar larvae were not affected by z3HOL treatment.For female TG,compared with the control tea plants,z3HOL-treated plants significantly influenced the larval life,pupal weight,and pupal width of TG.Those fed on z3HOL-treated tea plants prolonged larval development of TG.The pupae had significantly lower mass and less width than those fed on control plants.?2?In total,318 up regulated?primed?genes were detected.Among these genes,58 were defense-related,including 6 key enzyme genes in the biosynthesis of jasmonic acid?JA?and ethylene,26 signal transduction genes,12 anti-insect responsive transcription factors,and 14genes related to direct and indirect defense-related genes.?3?To validate the results of DEG analysis,20 DEGs were used in qRT-PCR to confirm the results of RNA-seq.The DEGs included 14 signaling transduction-related genes and six defense response-related16 genes.The results showed that all these genes were induced by TG infestation.Furthermore,except CBP2 and lectin-RLK1,while the expression levels of the remaining 18 genes were significantly upregulated in TG-infested z3HOL-primed tea plants compared with those in TG-infested tea plants.The results showed that except WRKY33 and bZIP genes,the remaining 18 DEGs were all induced by JA and wound treatment.From the six defense response-related genes,five were induced by ACC.Taken together,our study showed that when the primed tea plants were infested with TG larva,these plants can strongly perceive the elicitors by several RLKs and Ca²⁺signal on the plasma membranes.The perception events rapidly activated MAPK cascades and/or WRKYs.Activating MPKs and WRKYs enhance transcript levels of defense signal biosynthesis-related genes,thus increasing the concentrations of JA and ethylene and resulting in an effective direct and indirect defense response.Meanwhile,the enhanced JA level can activate the early signal transduction genes such as RLKs and Ca²⁺,thereby providing a positive feedback loop for the amplification of the signal cascades to enhance plant defense responses.