Research On The Mechanism Of Tobacco Resistance To Meloidogyne Incognita Invasion

Tobacco root knot nematode disease is one of the most important diseases in tobacco production,which widespread in tobacco-growing area domestic and overseas,causing economic losses annually.In the case of tobacco,Meloidogyne incognita(M.incognita)in particular is the most harmful.The development of resistant genotypes is an alternative strategy to effectively control these losses.Here,resistant(Yuyan12)and susceptible(Changbohuang)tobacco varieties were used as experimental materials.To compare the transcriptional regulation pattern in resistant and susceptible varieties,transcriptome sequencing technology was implemented for analyzing metabolic pathways related to nematode resistance.The changes of physiological indexes corresponding metabolic processes were researched to verify transcriptome sequencing results.Therefore,key physiological pathways and regulatory genes related to nematode resistance in tobacco were excavated from epigenetics and transcriptional inheritance.In addition,our results will facilitate to reveal physiological and molecular mechanisms to M.incognita in Yuyan12.The main results are as follows:1.Yuyan12 and Changbohuang showed different resistance to M.incognita.After inoculation with M.incognita,the average disease index of 1.35 and 78.23 were obtained for Yuyan12 and Changbohuang,respectively.M.incognita invasion significantly reduced the physiological functions of roots and leaves in Changbohuang,but had little effect on Yuyan12 which was no significant difference between inoculated and uninoculated samples.Hence,Yuyan12 was considered resistant and Changbohuang was considered susceptible genotypes.2.By comparing the transcriptome data of two varieties,an average of approximately 46 555 601 clean reads was generated with approximately 83% of the sequence successfully mapping to the reference genome.The data in each library were more than 6.49 G with 150-bp paired-end reads,and Q30 percentages are above 90.10%.According to the screening principle of differentially expressed genes(DEGs),2623 and 545 DEGs in M.incognita-infected roots were observed in Yuyan12 and Changbohuang,respectively,compared to those in non-infected roots,including 289 DEGs commonly expressed in the two genotypes.3.Functional annotation and enrichment analysis were conducted on 289 common DEGs in resistant and susceptible tobacco varieties to further elucidate the gene function.Among these DEGs,genes encoding cell wall modifying proteins,protein kinases,antioxidant systems,phenylpropanoid metabolism,hormone signal transduction and transcription factors involved in various biological and physiochemical processes related nematode resistance were significantly expressed in both genotypes.Meanwhile,a hypothetical model of resistance response to M.incognita in tobacco was drawn,and the results provide important information on the mechanism of tobacco resistance to M.incognita.4.Effects of M.incognita invasion on antioxidant system in Yuyan12 and Changbohuang were studied.After M.incognita invasion,O2-and MDA content in Changbohuang were significantly higher than those in Yuyan12,meanwhile,SOD?POD?CAT?GSH?GSSG and GR content in Yuyan12 were significantly higher than those in Changbohuang.Those results indicated that Yuyan 12 could rapidly produce peroxide reaction after M.incognita invasion,and it reduced the degree of membrane lipid peroxidation with a stronger active oxygen scavenging function.5.Effects of M.incognita invasion on phenylaprapanoid metabolism in Yuyan12 and Changbohuang were investigated.M.incognita invasion induced dramatic increase in PAL?TAL and PPO content of Yuyan12 and Changbohuang.In addition,PAL?TAL and PPO content in Yuyan12 were significantly higher than those in Changbohuang.These results suggested that phenylpropane metabolic processes could prevent nematode invasion by producing toxicant or lignification cell walls.In a word,phenylaprapanoid metabolism played an important role in preventing nematode invasion in Yuyan12.6.Effects of M.incognita invasion on endogenous hormones in Yuyan12 and Changbohuang were researched.Compared to the control treatment,CTK?IAA and JA content decreased in the early stage of M.incognita invasion.In Yuyan12,GA content increased but ABA content decreased.However,GA content decreased but ABA content increased in Changbohuang.The lower ABA and higher IAA content in Yuyan 12 might explain why its roots and leaves were not greatly affected by M.incognita invasion.In addition,the higher ABA and lower IAA content in Changbohuang could favor the formation of giant cells and provide favorable conditions for nematode proliferation.Therefore,tobacco endogenous hormones might play important regulatory roles in controlling nematode proliferation.