| The whitefly Bemisia tabaci is a global major agricultural pest,which seriously harms many economic crops and garden flowers.The whitefly rapid invasion of into China in recent years is mainly due to: When B.tabaci feed on plants,host plants mistake the feeding of B.tabaci for disease infection,thus activating SA(salicylic acid)defense response and inhibiting JA(jasmonic acid)defense response,making the plants more vulnerable to insect damage.It has been proved that the tomato volatile β-myrcene induced by B.tabaci can interfere with the anti-insect defense of neighboring plants.Through manipulating the chemical communication between plants,the population of B.tabaci spreads rapidly.However,the molecular mechanism of how the volatile β-myrcene interacts with different defense pathways,and therafter,inhibits theanti-insect defense response is still unclear.In this study,B.tabaci and its field host tomato were used as the research model system.Firstly,the effects of B.tabaci feeding on the release of volatile compounds in different tomato varieties were compared,and the differences of β-myrcene emission induced by B.tabaci in tomato varieties were determined.Secondly,the dynamic changes of JA pathway defense genes,JA-SA regulatory factors and endogenous plant hormones(JA,JA-ILe and SA),as well as the development of B.tabaci adults and nymphs were compared between the β-myrcene exposure treatment and the control treatment.Finally,virus-induced gene silencing(VIGS)technology was used to silence the regulatory factors that may interact with β-myrcene,and consequently to verify their key roles involved in β-myrcene-mediated anti-insect defenses in tomato.The specific research results are as follows1.Difference analysis of volatiles emission induced by B.tabaci among tomato varieties and its effect on tomato insect resistanceBy comparing the composition of volatiles induced by B.tabaci feeding on different tomato varieties,including Moneymaker(MM),Micro-Tom(MT),Castlemart(CM)and Alisa,we found that: more emission of β-myrcene andβ-caryophyllene were released from infested MM or MT plants compared with its uninfested plants.While infested Alisa plants only released more emission ofβ-myrcene compared with uninfested plants.In contrast,B.tabaci infestation had no effect on the volatiles release of CM plants.These results suggest that more emission of β-myrcene induced by B.tabaci feeding might be a widespread phenomenon in tomatoes.Secondly,the healthy MM plants were treated with different concentrations of β-myrcene,and the development of B.tabaci adults and nymphs were determined.The results showed that,regardless of the dose of β-myrcene,the fecundity of adults and the developmental rate of nymphs were significantly increased,but the survival rate of adults did not change significantly.These results indicated that the β-myrcene induced by B.tabaci could regulate the information transfer between tomato plants,reduce the anti-insect resistance of neighboring tomato plants,and promote the rapid reproduction of whiteflies.2.Effects of β-myrcene exposure on anti-insect defense and the expression of regulatory factors mediating the JA-SA interaction in tomatoThree genes related to insect resistance,Mi-1.2,PI-I and PI-II,were down-regulated in tomato pre-exposed with different concentrations of β-myrcene when the plants were subjected to different periods of B.tabaci feeding.The expression of Mi-1.2,PI-I and PI-II was significantly down-regulated in whitefly-infested plants pre-exposed with 200 μg or 400 μg of β-myrcene,respectively.The gene expression results of WIPK and NPR1,as regulators of JA-SA interaction,were completely different after β-myrcene treatment.β-myrcene exposure treatment had no significant effect on WIPK gene expression,but caused a significant suppression of NPR1 gene.In addition,β-myrcene exposure treatment also no effect on the expression of upstream JA-responsive gene AOC,but significantly down-regulated the expression of downstream JA-responsive gene MYC2.β-myrcene exposure treatment also had a certain effect on the accumulation of endogenous plant hormones,including JA,JA-ILe and SA,in tomato.Three β-myrcene exposure treatment all inhibited the accumulation of JA and JA-ILe.The accumulation of SA in the β-myrcene exposure treatment increased significantly 48 h after B.tabaci feeding.These results suggest that whitefly-induced β-myrcene can inhibit the JA-regulated anti-insect defenses,and MYC2 and NPR1 genes may play a key role in the inhibition of tomato defense response mediated by β-myrcene.3.Study on the function of NPR1 or MYC2 in the regulation ofβ-myrcene-meidatedanti-insect defenses in tomatoThrough using the technology of virus-induced gene silencing,the expression of NPR1 or MYC2 gene was suppressed.The effects of the NPR1 or MYC2 gene silencing on the expression of insect resistance gene,endogenous hormone accumulation,the development of adult and nymph were compared and analyzed.The results showed that,when NPR1 was silenced,β-myrcene exposure treatment had no effects on the expression of defense genes Mi-1.2,PI-I and PI-II,as well as the accumulation of endogenous JA and JA-ILe.Compared with the control treatment,the fecundity development rate of B.tabaci in the β-myrcene exposure treatment were not significantly changed.However,when MYC2 was silenced,β-myrcene exposure treatment suppressed the expression of Mi-1.2,PI-I and PI-II,and decreased the accumulation of JA and JA-ILe.Meanwhile,the adult fecundity development rate were significantly increased in the β-myrcene exposure treatment.These results suggest that the interaction between NPR1 and β-myrcene plays a key role in theβ-myrcene-mediated suppression of anti-insect defenses in tomato. |
