| Chinese jujube (Ziziphus jujuba Mill.) ranks the first place among the dry fruits interms of production in China. Jujube witches’ broom (JWB) disease, caused byphytoplasma (formerly called mycoplasma like organism or MLO), is a highly destructiveand strong infectious quarantine disease of Chinese jujube, and has become one of themost serious obstacles for sustainable development of jujube industry. Leaf yellowing isone of the main symptoms of JWB. Previous studies showed that the chlorophyll contentand photosynthetic capacity of plant leaf was significantly decreased after phytoplasmainfection. However, there was still lack of systematic and in-depth research of the effect ofphytoplasma on jujube photosynthesis, and the relationship between photosynthesis andthe resistance to JWB has not been reported. Photosynthesis is the basis of plant materialsynthesis and metabolism. The jujube cultivars with different resistance to JWB (resistantcultivar ‘Xingguang’ and susceptible cultivar ‘Pozao’) were used to compare theirdifferences in photosynthesis at metabolic and molecular levels after phytoplasma infection.The goals of this study were to reveal the relationship between photosynthesis and JWBresistance and provide a theoretical reference for JWB-resistant breeding in Chinese jujube.Meanwhile, based on the theory of plant induced resistance, we performed the resistanceinduction of susceptible cultivar ‘Dongzao’ to JWB, and tried to explore the mechanism ofinduced resistance. The main results were as follows:1. Five photosynthesis-related genes (ZjGluTR, KF530842; ZjCBP, KF530838;ZjRubisco, KF530841; ZjRCA1, KF530839; ZjRCA2, KF530840) of Chinese jujube werefirstly cloned and registered in Genebank.2. Two RCA genes were cloned by us in this study and ZjRCA2plays important rolein Rubisco activation.3. The relative content of phytoplasma in resistant and susceptible cultivars wasmeasured in different infection stages by real-time quantitative PCR technology. Theresults showed that along with the infected time the content of phytoplasma and its activityin susceptible cultivar ‘Pozao’ increased rapidly. But in resistant cultivar ‘Xingguang’, thephytoplasma was detected only at later infected stages with small amount and has no activity.4. The photosynthetic pigment (chlorophyll and carotenoids) contents in infectedleaves were detected. The content of photosynthetic pigment in infected ‘Pozao’ wassignificantly lower than that of non-infected control after middle infected stage. But inresistant cultivar ‘Xingguang’, the content of photosynthetic pigments was significantlyhigher than non-infected one at the early and middle infected stages.5. The chlorophyll fluorescence parameters in resistant and susceptible cultivars weremeasured, respectively. The results showed that the photosynthetic activity and potentialactivity of photosystemⅡ (Fv/Fm, ΦPSII, Fv/Fo) in infected ‘Pozao’ decreased markedlythan those of control from15to18weeks after grating infection. But in infected‘Xinguang’, the parameters were significantly lower than those of control at initial infectedstage.6. By using qRT-PCR technology, we found that the photosynthetic-related genes(ZjGluTR, ZjCBP, ZjRubisco and ZjRCA2) in susceptible cultivar ‘Pozao’ showed amarkedly down-regulated trend at later infected stages (from12to18weeks after grafting).But in resistant cultivar ‘Xingguang’, those genes were obviously up-regulated at thisstage.7. The difference between resistant and susceptible cultivars in photosyntheticresponse patterns suggests that photoinhibition occurred in ‘Xingguang’ belongs tophotoprotection, but in ‘Pozao’, the photoinhibition belongs to photosystem II damage.Moreover，the response mechanism of ‘Xingguang’ related to it’s resistance to jujubewitches’ broom disease.8. Take the advantages of induction method integrating micro-grafting infection andkilling pathogen, susceptible ‘Dongzao’ plantlets were used as materials to inducedresistance to JWB. Then we acquired59plantlets with once resistance induction,63plantlets with twice resistance induction and135plantlets with three times resistanceinduction. The expression levels of the resistance-related genes (ZjNBS-LRR, ZjCIPK,ZjERF, ZjbZIP, ZjTLP, ZjPR10, ZjHSP) in the induced-resistance materials were graduallyincreased with the increasing of induction times, and the disease resistance of plantlets alsoenhanced accordingly.9. The plantlets with different induction times were further analyzed by67pairs ofSSR primer, and no difference among those plantlets was found. The result indicated thatthe induced resistance plantlets have no mutation in genome level or mutation occurredonly in point which difficult to detect. |
PDF Full Text Request