The OsmiR396–OsGRF8–OsF3H‐flavonoid pathway mediates resistance to the brown planthopper in rice (Oryza sativa)

Cong Zhou,Zhengyan Dai,Fang Yang,Jiang Tan,Shichen Sun,Xiaofang Yang,Zhenying Shi,Xuexia Miao,Shijuan Zhang

doi:10.1111/pbi.13091

Abstract

SummaryMulti‐functional microRNAs (miRNAs) are emerging as key modulators of plant–pathogen interactions. Although the involvement of some miRNAs in plant–insect interactions has been revealed, the underlying mechanisms are still elusive. The brown planthopper (BPH) is the most notorious rice (Oryza sativa)‐specific insect that causes severe yield losses each year and requires urgent biological control. To reveal the miRNAs involved in rice–BPH interactions, we performed miRNA sequencing and identified BPH‐responsive OsmiR396. Sequestering OsmiR396 by overexpressing target mimicry (MIM396) in three genetic backgrounds indicated that OsmiR396 negatively regulated BPH resistance. Overexpression of one BPH‐responsive target gene of OsmiR396, growth regulating factor 8 (OsGRF8), showed resistance to BPH. Furthermore, the flavonoid contents increased in both the OsmiR396‐sequestered and the OsGRF8 overexpressing plants. By analysing 39 natural rice varieties, the elevated flavonoid contents were found to correlate with enhanced BPH resistance. Artificial applications of flavonoids to wild type (WT) plants also increased resistance to BPH. A BPH‐responsive flavanone 3‐hydroxylase (OsF3H) gene in the flavonoid biosynthetic pathway was proved to be directly regulated by OsGRF8. A genetic functional analysis of OsF3H revealed its positive role in mediating both the flavonoid contents and BPH resistance. And analysis of the genetic correlation between OsmiR396 and OsF3H showed that down‐regulation of OsF3H complemented the BPH resistance characteristic and simultaneously decreased the flavonoid contents of the MIM396 plants. Thus, we revealed a new BPH resistance mechanism mediated by the OsmiR396–OsGRF8–OsF3H–flavonoid pathway. Our study suggests potential applications of miRNAs in BPH resistance breeding.

Highlights

Non-protein-coding RNAs are widespread and more common than previously thought (Morris and Mattick, 2014)
Because the miRNAs are so functionally diverse, we investigated whether they are involved in brown planthopper (BPH) resistance
We mainly focused on OsmiR396b

Summary

Introduction

Non-protein-coding RNAs are widespread and more common than previously thought (Morris and Mattick, 2014). MicroRNAs (miRNAs) of approximately 22 nucleotides in length regulate gene expression through antisense complementary binding to mRNAs at the post-transcriptional level by their simple core mechanism (Ambros, 2001; Nelson et al, 2003). Large numbers of miRNAs are involved in biotic and abiotic stress responses (Khraiwesh et al, 2012; Sunkar and Zhu, 2004), the underlying mechanisms remain largely elusive. In rice (Oryza sativa), miR319 mediates response to rice ragged stunt virus by regulating the jasmonic acid (JA) biosynthetic and signalling pathways (Zhang et al, 2016). The roles of plant miRNAs in plant–insect interactions and their underlying mechanisms have rarely been studied

Results

Discussion

Conclusion