Overexpression of an Osa-miR162a Derivative in Rice Confers Cross-Kingdom RNA Interference-Mediated Brown Planthopper Resistance without Perturbing Host Development

Rice is a main food crop for more than half of the global population. The brown planthopper (BPH, Nilaparvata lugens) is one of the most destructive insect pests of rice. Currently, repeated overuse of chemical insecticides represents a common practice in agriculture for BPH control, which can induce insect tolerance and provoke environmental concerns. This situation calls for innovative and widely applicable strategies for rice protection against BPH. Here we report that the rice osa-miR162a can mediate cross-kingdom RNA interference (RNAi) by targeting the NlTOR (Target of rapamycin) gene of BPH that regulates the reproduction process. Through artificial diet or injection, osa-miR162a mimics repressed the NlTOR expression and impaired the oviposition of BPH adults. Consistently, overproduced osa-miR162a in transgenic rice plants compromised the fecundity of BPH adults fed with these plants, but meanwhile perturbed root and grain development. To circumvent this issue, we generated osa-miR162a-m1, a sequence-optimized osa-miR162a, by decreasing base complementarity to rice endogenous target genes while increasing base complementarity to NlTOR. Transgenic overexpression of osa-miR162a-m1 conferred rice resistance to BPH without detectable developmental penalty. This work reveals the first cross-kingdom RNAi mechanism in rice-BPH interactions and inspires a potentially useful approach for improving rice resistance to BPH. We also introduce an effective strategy to uncouple unwanted host developmental perturbation from desirable cross-kingdom RNAi benefits for overexpressed plant miRNAs.

Identification of two QTLs, BPH41 and BPH42, and their respective gene candidates for brown planthopper resistance in rice by a combinatorial approach of QTL mapping and RNA-seq

The brown planthopper (BPH) is the leading cause of insect damage to rice plants. It has caused profound losses in rice production since the late 1970’s and continues to be a major pest problem. Therefore, there is an urgent need to discover new BPH resistance genes to ensure the successful production of rice. Here, a new BPH resistance source provided by SeedWorks International Pvt. Ltd., SWD10, was used for this purpose. A total of 232 F2 progenies were genotyped with 216 polymorphic markers. Results revealed two dominant QTLs located on the short and long arms of chromosome 4. These QTLs are referred to as BPH41 and BPH42, respectively. BPH resistance mechanism test revealed that antibiosis and antixenosis mechanisms both play a role in BPH resistance conferred by these two QTLs. To further reduce the size of each QTL, 14,368 recombinant lines were screened, and the QTLs were delimited between markers SWRm_01617 and SWRm_01522 for BPH41, and SWRm_01695 and SWRm_00328 for BPH42. Additionally, using RNA-seq data of lines containing the QTLs, we further shortlisted four and three gene candidates for BPH41 and BPH42, respectively. Differential gene expression analysis of lines containing the QTLs suggested that SWD10 BPH resistance is contributed by the plant’s innate immunity and the candidate genes may be part of the rice innate immunity pathway. The newly identified QTLs are currently being utilized for breeding BPH resistant rice varieties and hybrids.

Evaluation of Rice Landraces for Brown Planthopper Resistance Based on Phenotypic Reactions and Biochemical Attributes

Brown planthopper (BPH), [Nilaparvata lugens (Stål.)] is an economically important pest of rice (Oryza sativa L.) throughout Asia, where the damage caused by nymphs and adults, especially during post-tillering to milking stages, significantly reduces grain yield. There is, thus, a pressing need to develop varieties that are resistant to BPH. In this study, the reaction of various rice landraces from Indian origin were assessed (both phenotypically and biochemically) in response to BPH infestation. It was found that the landraces, viz. Badshabhog, Gamra, Haldichuri, Janglijata, Kalabhat, Khara, Adanshilpa, Chikonmashuri, Kerala sundari and Lal dudheshwar exhibited resistance to BPH consistently along with the standard check Ptb33, for three consecutive years under both greenhouse and open-field conditions. These phenotypically resistant rice landraces including Ptb33 exhibited lowest feeding rate, least nymphal and adult preference, minimum survival and higher frequency (%) of unhatched eggs when compared with the susceptible check (Swarna). Higher levels ascorbic acid, oxalic acid (OA), crude silica (CS), while lower levels of phenols, reducing sugar and total free amino acid (TFA) were expressed in un-infested resistant and moderately resistant landraces. The resistant plants exposed to herbivory by BPH produced higher levels of phenolic compounds, potassium and TFA than plants of susceptible cultivar Swarna. The feeding rate, settling behaviour and survivability of BPH correlated significantly and negatively with OA and CS, whereas the latter showed a significant and positive correlation with egg hatchability.