Fine Mapping and Analysis of Pyramiding Effects of Rice Brown Planthopper Resistance Genes QBPH1 and QBPH4

This study aims to discover new quantitative trait loci (QTLs) for resistance to the brown planthopper (BPH) in rice by utilizing a genetic population and to assess the pyramiding effects of these QTLs, thereby providing crucial genetic materials and resources for breeding insect-resistant rice.

A recombinant inbred line (RIL) population derived from a cross between susceptible NPB and resistant Jiafuzhan was used, combined with seedling stage resistance evaluation and extreme mixed pool sequencing (BSA-seq) to map BPH resistance QTLs. Further, fine mapping, candidate gene identification, pyramiding effect analysis, and mixed-pool transcriptome sequencing (BSR-seq) were employed to elucidate the physiological and molecular mechanisms mediated by these QTLs.

BSA-seq identified two major resistance QTLs on chromosomes 1 (30-32 Mb) and 4 (5-7 Mb), named QBPH1 and QBPH4, respectively. Interval-linked molecular markers confirmed the authenticity of these QTLs. QBPH4 coincides with previously cloned BPH3 and BPH15, while QBPH1 represents a newly discovered QTL. High-density markers and recombinant analysis further narrowed the QBPH1 region to 30.61-30.65 Mb. This analysis identified Os01g53294 and Os01g53330 as reliable candidate genes, which code for a respiratory burst oxidase protein B and an anthocyanin 5,3-O-glucosyltransferase, respectively. In evaluations of seedling resistance, brown planthopper honeydew area and weight, insect weight gain, lethality, and preference, comparisons between QBPH1 and QBPH4 single genes and their polymerized lines revealed no significant enhancement in resistance. Both QBPH1 and QBPH4 mediated antibiosis and antixenosis mechanisms with varying effects. BSR-seq analysis highlighted significant enrichment of differentially expressed genes (DEGs) involved in transcriptional regulation, protein phosphorylation, and redox processes among different QBPH1 alleles. Additionally, genes associated with jasmonic acid (JA) synthesis and signaling pathways were significantly upregulated in resistant materials, confirmed by RT-qPCR experiments.

A novel BPH resistance QTL, QBPH1, was successfully identified on chromosome 1 of rice. QBPH1 mediated both antibiosis and avoidance against BPH, though its aggregation effect with another QTL was not significant. QBPH1 may mediate defense mechanisms against BPH through involvement in the JA pathway. Based on this, Os01g53294 and Os01g53330 have been validated as reliable candidate genes for QBPH1.