| Southern rice black-streaked dwarf virus(SRBSDV) and Rice ragged stunt virus(RRSV) is respectively transmitted by white-backed planthopper(WBPH) andbrown planthopper(BPH),Previous research has shown that SRBSDV-infected rice plants had increased attraction to virus-free WBPH and RRSV-carrying BPH, but decreased attraction to viruliferous WBPH andvirus-free BPH. In order to clear the relationship between the attraction of rice plant to Rice Planthoppers and disease progression, we conducted host selection preference tests using Y-shape olfactometer and Free choice device at different stages ofdisease progression,and then analyzed the virus titer and the expression level of defense and volatile synthesis-related genes(Os AOS1?Os ICS?Os ACS2?Os LIS?Os CAS?Os HPL3) of SRBSDV and RRSV-infected rice plants with RT-q PCR.The results as follows:(1) It was indicated that SRBSDV or RRSV infection alter the attractiveness of rice plant to Vector and Non-vector Rice Planthoppers,and the attractiveness was mainly mediated byrice volatiles,varied with disease progression. We tested the attractiveness of the SRBSDV-infected plants or RRSV-infected plants to virus –free WBPH or BPH using Y-shape olfactometer and Free choice device,the results indicated that the infected rice plants showed the attractiveness change of first weakened, then enhanced and last weakened again.Particularly atabout 40 days after SRBSDV-infected or 45 days after RRSV-infected,the infected rice plantshowed the strongest attraction to Vector and Non-vector Rice Planthoppers. The results of the Y-shape olfactometer tests were essentially the same as the Free choice device tests,it showed that the effects of rice on Planthoppers ' host selection preference behaviors were mainly mediated by rice volatiles.(2)It was indicated that the host selection preference of the virus-carrying Planthoppers changed greatly compared to the virus-free Planthoppers. Generally speaking, the SRBSDV-carrying WBPH preferred the healthy plants and the RRSV-infected plants; the RRSV-carrying BPH preferred the healthy plants and the SRBSDV-infected plants.But the host selection preference behavior of the virus-carying Planthoppers were not fully consistent between the Y-shape olfactometer and Free choice device,and the differences varied with disease progression, such as at 35 days after SRBSDV-infected or 20 days after RRSV-infected,the SRBSDV-carrying WBPH and the RRSV-carrying BPH preferred the healthy plants in Y-shape olfactometer tests,but preferred the virus-infected plants in Free choice. It was indicated that other factors took part in the host selection behaviors of the virus-carrying Planthoppers besides the olfactory.(3) It was indicated that the attractiveness of SRBSDV or RRSV-infected plants to the Planthoppers was positively linearly correlated with its virus titer, its effects on virus-free planthoppers were more prominent than virus-carrying planthoppers. The attractiveness of SRBSDV or RRSV-infected plant to virus-free WBPH or virus-free BPH increased as increasing virus content,the virus titer reached a maximum respectively at about 40 days(SRBSDV) or 45 days(RRSV),Meanwhile, the attractiveness also reached the strongest state.The infected plants showed increased attraction to virus-carrying Planthoppers only when the virus titer reached a higher level,and the attractiveness of SRBSDV or RRSV-infected plant to virus-carrying non-vector Planthoppers was stronger than the virus-carrying vector Planthoppers,such as at about 40 days after infection,60% of the SRBSDV-carrying WBPH and 82% of the RRSV-carrying BPH preferred the SRBSDV-infected plants;At about 45 days after infection,44% of the RRSV-carrying BPH and 64% of the SRBSDV-carrying WBPH preferred the RRSV-infected plants. Generally speaking, the attractiveness of the infected plants to the virus-free Planthoppers was weaker than the healthy plants,but the attractiveness to the virus-carrying non-vector Planthoppers was stronger than the healthy plants.(4) It was indicated that the attractiveness of the SRBSDV or RRSV-infected plants to WBPH or BPH were irrelevant to its chlorophyll relative content.At 15-50 days after virus infection, the chlorophyll relative content of the infected plants were higher than the healthy plants,and reach to significant difference in individual points such as at 15,20,25 and 50 days after RRSV-infected,the RRSV-infected plants showed significantly increased attraction to the RRSV-carrying BPH at 20 days,but decreased attraction at 25 days,and increased attraction at 50 days.It thus can be seen that the vision mediated bychlorophyllin leaveshad not taken a lead role in thehost selection behavior.(5) It was indicated that the significantly enhanced attractiveness of SRBSDV or RRSV-infected plants to WBPH or BPH were related to the expression level of defense and volatile synthesis genes.According to RT-q PCR results,compared to the healthy plant,at about 40 days after SRBSDV-infected,SRBSDV-infected plants cut their expression levels of Os AOS1?Os ICS and Os ACS2 respectively by about 79.7%?46.3% and 23.8%,but raised their expression levels of Os LIS?Os CAS and Os HPL3 respectively by about282.2%?73.4% and 209.2%.at about 45 days after RRSV-infected, RRSV-infected plants cut their expression levels of Os AOS1?Os ICS and Os ACS2 respectively by about 63.3% ?35.5% and 25.2%,but raised their expression levels of Os LIS?Os CAS and Os HPL3 respectively by about114.4%?41.7% and 191.7%,so the down regulation of Os AOS1?Os ICS and Os ACS2 means the weakening of defense responses in the SRBSDV or RRSV infected plants, the up regulation of Os LIS?Os CAS and Os HPL3 means the enhancing of volatile release levels in the SRBSDV or RRSV infected plants.Down-regulated Os AOS1?Os ICS?Os ACS2 and up-regulated Os LIS?Os CAS?Os HPL3 in SRBSDV or RRSV-infected rice plants were linked to accelerated attraction.Our study highlights potential strategies of SRBSDV and RRSV in enhancing their transmission, and provides new insights into the complexity of virus-vector interactions. |
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