Abstract
Fitness cost is a common phenomenon in rice blast disease-resistance breeding. MiR396 is a highly conserved microRNA (miRNA) family targeting Growth Regulating Factor (OsGRF) genes. Mutation at the target site of miR396 in certain OsGRF gene or blocking miR396 expression leads to increased grain yield. Here we demonstrated that fitness cost can be trade-off in miR396-OsGRFs module via balancing growth and immunity against the blast fungus. The accumulation of miR396 isoforms was significantly increased in a susceptible accession, but fluctuated in a resistant accession upon infection of Magnaporthe oryzae. The transgenic lines over-expressing different miR396 isoforms were highly susceptible to M. oryzae. In contrast, overexpressing target mimicry of miR396 to block its function led to enhanced resistance to M. oryzae in addition to improved yield traits. Moreover, transgenic plants overexpressing OsGRF6, OsGRF7, OsGRF8, and OsGRF9 exhibited enhanced resistance to M. oryzae, but showed different alteration of growth. While overexpression of OsGRF7 led to defects in growth, overexpression of OsGRF6, OsGRF8, and OsGRF9 resulted in better or no significant change of yield traits. Collectively, our results indicate that miR396 negatively regulates rice blast disease- resistance via suppressing multiple OsGRFs, which in turn differentially control growth and yield. Therefore, miR396-OsGRFs could be a potential module to demolish fitness cost in rice blast disease-resistance breeding.
Highlights
Plants are often targeted by pathogens such as bacteria, fungi, and oomycetes, and as a part of evolution, they developed complex network comprising pathogen-associated molecular pattern- (PAMP)-triggered immunity (PTI) and Effector-triggered immunity (ETI), to counteract the pathogens (Ramirez-Prado et al, 2018)
The miR396 overexpression and STTM396 transgenic lines were obtained from a previous study (Li et al, 2016); and miR396 target mimic (MIM396) and OsGRF overexpression transgenic lines were obtained from a previous study (Gao et al, 2016)
In order to elucidate the differential responses of miR396 isoforms to M. oryzae infection, we analyzed their expression in the susceptible line LTH and the monogenic resistant line IRBLkm-Ts that contains the resistance (R) gene Pi-km and exhibits high resistance to M. oryzae isolates carrying AVR-Pikm (Li et al, 2014)
Summary
Plants are often targeted by pathogens such as bacteria, fungi, and oomycetes, and as a part of evolution, they developed complex network comprising pathogen-associated molecular pattern- (PAMP)-triggered immunity (PTI) and Effector-triggered immunity (ETI), to counteract the pathogens (Ramirez-Prado et al, 2018). MiR393 regulates host immunity against Pseudomonas syringae DC3000 by suppressing auxin signaling through targeting the auxin receptors such as TIR1, AFB2, and AFB3 (Navarro et al, 2016). MiR396 Balances Rice Immunity and Growth as negative regulators of immunity against bacterial infection in Arabidopsis (Fahlgren et al, 2007; Jagadeeswaran et al, 2009; Li et al, 2010). MiR482 regulates host defense by targeting coiled-coil-nucleotide-binding leucine-rich-repeat (CC-NB-LRR)-encoding transcripts and triggers the production of secondary siRNAs via RDR6, which in turn targets other mRNAs of defense related genes (Shivaprasad et al, 2012). Md-miRLn11 regulates NBS-LRR gene expression upon apple leaf spot fungal infection (Ma et al, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
