Induced-responses Of The Chilo Suppressalis To Resistant Rice Cultivars And The Expression Pattern Of Chitinase Gene OsCHIT15

The striped stem borer,Chilo suppressalis?Walker?is one of the most serious pests in rice production in China,causes annual loses of hundreds of millions of yuan.Effective management of striped stem borer mainly depends on synthetic chemical insecticides.As a consequence of over-application of insecticides for C.suppressalis management,environmental pollution and reductions in insecticide efficacy have been reported.Thus,it is imperative to develop and promote new environmentally friendly control technologies Screening and breeding of resistant cultivars could control pests effectively without negative affecting the environment,in which plant defense mechanisms and genetic engineering techniques induced by herbivorous insect feeding are effective and feasible.Chitinase,an insect molting enzyme which degrades chitin to a lower molecular weight as oligosaccharides and affects the digestive system of insects has been developed as a research hotspot in current plant pest-resistant genetic engineering.The three rice genetic lines 1688,1665 and 1654 were commonly planted in Northeast China used as experimental materials in this study,C.suppressalis larvae were fed with or without the addition of different cultivars of rice plant powder,and after 10 days,the survival rate and larval weight were observed.The activities of three protective enzymes in C.suppressalis larvae of different rice cultivars were determined.The full-length expression of rice chitinase gene Os CHIT15 was cloned,sequence and phylogenetic analyses were performed,and the spatiotemporal expression patterns of Os CHIT15 in response to C.suppressalis artificial infestation and mechanical treatment were systematically determined at rice seeding and tillering stage,speculate on the relationship between the expression level of Os CHIT15 gene and rice resistance.The results are as follows:1.After C.suppressalis larvae were fed with addition of 1654 rice stem powder for 10 days,the weight of the larvae was not significantly different from that fed with the the addition of 1665 powder,but significantly lower than the other groups.After C.suppressalis larvae were fed the stem of 1654,the activity of CAT decreased after the increase to the maximum,and the activity of POD and SOD fluctuated.The activity of protective enzymes in the C.suppressalis was fed 1665 did not change much.The protective enzyme activity of larvae increased most after feeding the stem of 1688.2.The full-length ORF sequence of Os CHIT15 is 2763 bp long and its open reading encodes 178 amino acids belongs to Chitinase class I?Glyco_hydro₁9 super family?.Sequence analysis shows Os CHIT15 and the chitinase of other Poaceae shares more than 80% identity.The results of phylogenetic trees indicate that chitinase in rice is clustered with chitinase from other Poaceae plants.3.The results of RT-q PCR showed that Os CHIT15 was constitutively expressed in three tested rice lines,suggesting that expression of Os CHIT15 is accompanied by the growth process of rice.Expression of Os CHIT15 is significantly induced by both C.suppressalis infestation treatment and mechanical treatment in three rice lines,but with different expression patterns in different tissues and different developmental stages.In the three rice lines,the 1654 exhibited a higher potential defense level,with a remarkable induction of Os CHIT15 expression by both C.suppressalis infestation and mechanical treatments,In the stems of rice seeding and tillering stage,the expression level of Os CHIT15 gene increased significantly within 12 hours after treatment.The inducing expression level of Os CHIT15 gene was less in 1665,and the inducing expression level in tillering stage was lower than that in seedling stage.In our study,the 1688 lineage showed different expression patterns across different developmental stages,Os CHIT15 showed a higher inducing expression in the tillering stage than in the seedling stageOur results demonstrate that the Os CHIT15 may be involved in defense responses induced by C.suppressalis and mechanical damage.This defense level in 1654 is higher than that in other rice lines,indicating that 1654 is a potential C.suppressalis resistant rice lineage that could be promoted and planted.