Abstract
BackgroundOutbreaks of insect pests in paddy fields cause heavy losses in global rice yield annually, a threat projected to be aggravated by ongoing climate warming. Although significant progress has been made in the screening and cloning of insect resistance genes in rice germplasm and their introgression into modern cultivars, improved rice resistance is only effective against either chewing or phloem-feeding insects.ResultsIn this study, the results from standard and modified seedbox screening, settlement preference and honeydew excretion tests consistently showed that Qingliu, a previously known leaffolder-resistant rice variety, is also moderately resistant to brown planthopper (BPH). High-throughput RNA sequencing showed a higher number of differentially expressed genes (DEGs) at the infestation site, with 2720 DEGs in leaves vs 181 DEGs in sheaths for leaffolder herbivory and 450 DEGs in sheaths vs 212 DEGs in leaves for BPH infestation. The leaf-specific transcriptome revealed that Qingliu responds to leaffolder feeding by activating jasmonic acid biosynthesis genes and genes regulating the shikimate and phenylpropanoid pathways that are essential for the biosynthesis of salicylic acid, melatonin, flavonoids and lignin defensive compounds. The sheath-specific transcriptome revealed that Qingliu responds to BPH infestation by inducing salicylic acid-responsive genes and those controlling cellular signaling cascades. Taken together these genes could play a role in triggering defense mechanisms such as cell wall modifications and cuticular wax formation.ConclusionsThis study highlighted the key defensive responses of a rarely observed rice variety Qingliu that has resistance to attacks by two different feeding guilds of herbivores. The leaffolders are leaf-feeder while the BPHs are phloem feeders, consequently Qingliu is considered to have dual resistance. Although the defense responses of Qingliu to both insect pest types appear largely dissimilar, the phenylpropanoid pathway (or more specifically phenylalanine ammonia-lyase genes) could be a convergent upstream pathway. However, this possibility requires further studies. This information is valuable for breeding programs aiming to generate broad spectrum insect resistance in rice cultivars.
Highlights
Outbreaks of insect pests in paddy fields cause heavy losses in global rice yield annually, a threat projected to be aggravated by ongoing climate warming
Qingliu is moderately resistant to brown planthopper infestation The standard seedbox screening test (SSST) showed that Qingliu was relatively less severely infested by BPH than the two susceptible cultivars Taichung Native 1 (TN1) (8.3) and TNG67 (7.0) (Table 1)
The modified seedbox screening test (MSST) revealed a consistent result with the SSST (Table 1). These results indicated that Qingliu is moderately resistant to BPH infestation
Summary
Outbreaks of insect pests in paddy fields cause heavy losses in global rice yield annually, a threat projected to be aggravated by ongoing climate warming. There are over 100 species of rice-feeding insect pests, of which approximately 20 species are considered major pests that severely affect rice yield [4]. Frequent and widespread outbreaks of major insect pests of rice, including the brown planthopper (BPH; Nilaparvata lugens) and rice leaffolder (Cnaphalocrocis medinalis), have caused losses of hundreds of millions of dollars annually and threatened food security [3, 5]. Insect pests cause severe damage to rice plants, as these pests thrive in the warm and humid environment of fertile paddy fields [6]. Insect pest infestations in paddy fields are predicted to become more rampant and serious in a warming climate that increases the metabolic rates and population growth of insects [7]
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