类黄酮合成通路介导的木薯对木薯绵粉蚧的防御机理

Flavonoid Synthesis Pathway-mediate Defense Mechanism of Cassava Against Phenacoccus manihoti

木薯是世界重要的粮食作物、能源作物和工业原料。木薯绵粉蚧(Phenacoccus manihoti Matile-Ferrero)是一种世界危险性检疫性害虫,培育和利用抗虫木薯品种可以有效阻断其定殖为害。挖掘具有抗虫作用的次生代谢物质及其调控基因是开展抗虫育种的重要策略之一。而类黄酮是植物抵御生物与非生物胁迫的特有次生代谢物质,但类黄酮及其合成通路基因在木薯抗木薯绵粉蚧中的功能尚不清楚。据此,本研究分析了抗虫木薯品种(C1115、SC9、缅甸)和感虫木薯品种(KU50、SC205、面包)被木薯绵粉蚧为害不同时间(0、1、4、8d)后,叶片中类黄酮合成通路相关基因(CHS、CHI、FLS、LAR、DFR、F3H、CCoAOMT、C4H、C3’H、ANR)表达量以及类黄酮含量的变化情况。结果表明:木薯绵粉蚧取食后,叶组织中CCoAOMT、C3’H、ANR、C4H虽然上调表达,但与为害前相比并无显著差异,且抗、感木薯品种间的表达量也无显著差异;与之相对,CHS、CHI、FLS、F3H、DFR、LAR基因表达量均比为害前显著提高,并且在相同的为害时间内,这6个基因在抗虫木薯品种中的表达量也显著高于感虫木薯品种。进一步通过相关性分析发现,CHS、CHI、FLS、F3H、LAR基因的表达量与木薯品种的抗虫性呈显著正相关。此外,总黄酮含量测定结果表明:木薯绵粉蚧为害1 d时总黄酮含量与为害前相比均显著上升,为害4 d后抗虫木薯品种总黄酮含量显著高于感虫木薯品种。相关性分析显示,总黄酮含量也与木薯品种的抗虫性呈显著正相关。因此推测,类黄酮含量的上升及其调控基因CHS、CHI、FLS、F3H、LAR在抗虫木薯品种中的显著上调表达与其对木薯绵粉蚧的抗性有关。本研究为深入解析类黄酮合成基因调控木薯对木薯绵粉蚧的抗虫防御反应分子机制,以及木薯抗虫分子设计育种提供重要的前期基础。

Cassava is an important food crop,energy crop and industrial raw material.Cassava mealybug(Phenacoccus manihoti Matile-Ferrero)is a dangerous quarantine pest in the world,the cultivation and utilization of insect-resistant cassava cultivars can effectively block its colonization.Mining insect-resistant secondary metabolites and the regulatory genes is one of the important strategies for insect-resistant breeding.Flavonoids are unique secondary metabolites for plants to resist biotic and abiotic stresses,but the function of flavonoids and the synthesis pathway genes in cassava resistance to cassava mealybug is still unclear.Based on this,this study analyzed the expression levels of flavonoid synthesis pathway-related genes(CHS,CHI,FLS,LAR,DFR,F3H,CCoAOMT,C4H,C3'H and ANR)and flavonoid content in the leaves of insect-resistant(C1115,SC9,Myanmar)and insect-susceptible(KU50,SC205 and Bread)cas-sava cultivars after being damaged by cassava mealybug for different time(0,1,4,8 d).Although the expression of CCoAOMT,C3'H,ANR and C4H in the leaf was up-regulated after feeding,there was no significant difference com-pared with that before damage,and there was no significant difference in the expression level between the resistant and susceptible cassava cultivars.In contrast,the expression levels of CHS,CHI,FLS,F3H,DFR and LAR genes were sig-nificantly higher than those before damage,and in the same damage time,the expression levels of the six genes in the insect-resistant cassava cultivars were also significantly higher than those in the insect-susceptible cassava cultivars.Further correlation analysis showed that the expression levels of CHS,CHI,FLS,F3H and LAR genes were significantly positively correlated with the insect resistance of cassava cultivars.In addition,the results of total flavonoid content determination showed that the total flavonoid content increased significantly after one day of damage compared with that before damage,and the total flavonoid content of insect-resistant cassava cultivars was significantly higher than that of the insect-susceptible cassava cultivars after 4 days of damage.Correlation analysis showed that the total flavonoid content was also significantly positively correlated with the insect resistance of cassava cultivars.Therefore,it is speculated that the increase of flavonoid content and the significantly up-regulation of CHS,CHI,FLS,F3H and LAR in the insect-resistant cassava cultivars may be related to the resistance to cassava mealybug.This study would provide an important preliminary basis for the in-depth analysis of the molecular mechanism of flavonoid synthesis genes regulat-ing the insect-resistant defense response of cassava to mealybug,as well as the molecular design and breeding of cas-sava insect-resistant.