miR396-OsGRFs Module Balances Growth and Rice Blast Disease-Resistance

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.

Characteristic Dissection of Xanthomonas oryzae pv. oryzae Responsive MicroRNAs in Rice

“…Among them, nearly 50% target genes were distributed in different transcription factors families, including SQUAMOSA PROMOTER BINDING-LIKE (SPL), MYB, AUXIN RESPONSE FACTOR (ARF), NAC, Homeobox (HB), GRAS, AP2, GROWTH-REGULATING FACTOR (GRF), AP2/EREBP and MADS, in which NAC and GRF family numbers may participate in rice immune response. For instance, osa-miR164a/OsNAC60 [16] and osa-miR396/OsGRFs [20] regulatory modules manipulate rice resistance to M. oryzae invasion. As for target genes encoding the regulatory or metabolic enzyme, 12 targets could be divided into biotic stress related genes (LOC_Os01g47530, LOC_Os03g02970 (OsDCL1), LOC_Os03g46570, LOC_Os09g20090, LOC_Os10g41590, LOC_Os08g33370), abiotic stress related genes (LOC_Os08g14440, LOC_Os10g35840) and others (LOC_Os12g10740, LOC_Os03g55010, LOC_Os03g55030, LOC_Os04g51400) by function annotation and sequence homology analysis.…”

“…Recent work accumulated several lines of evidence that miRNAs/targets unit is an irreplaceable regulatory strategy in rice and pathogens interaction. To date, osa-mi169a/OsNF-YA [18], osa-miR166k-5p/OsEIN2 [14], osa-miR319b-OsTCP21 [19], osa-miR164a/OsNAC60 [16], osa-miR396/OsGRFs [20] and osa-miR167d/ARF12 [17] units have been reported to participate in defense under the pressure of M. oryzae in rice. Moreover, osa-mi319/OsTCP21 [27], osa-miR444/OsMADS57 [26], osa-miR171b/OsSCL6-IIa, OsSCL6-IIb, OsSCL6-IIc [25] and osa-miR528/OsAO [24] regulatory units could change the disease development caused by rice stripe virus and rice ragged stunt virus, respectively.…”

“…In rice blast, Magnaporthe oryzae (M. oryzae), the causal fungal agent, invasion rewrites the rice immune system by inducing or suppressing the expression of numerous miRNAs. Several groups have experimentally confirmed that the transgenic rice with overexpression of osa-miR160a [13], osa-miR166k [14], osa-miR398b [13] and osa-miR7695 [15] enhance the resistance to M. oryzae, while the osa-miR164a [16], osa-miR167d [17], osa-miR169a [18], osa-miR319 [19] and osa-miR396 [20] negatively regulate rice immunity against the blast fungus. Likewise, comprehensive analysis of miRNAs roles in rice sheath blight has also been investigated to uncover the pathogenic mechanisms of Rhizoctonia solani (R. solani) [21], and only one paper, to date, reported that osa-miR164a promoted the rice susceptibility to R. solani by targeting the OsNAC60 [16].…”

circRNAs Are Involved in the Rice-Magnaporthe oryzae Interaction

“…Genome-wide small RNA analyses have revealed a number of candidate miRNAs responsive to M. oryzae infection or elicitors (Campo et al, 2013;Li et al, 2014;Li et al, 2016;Wang et al, 2018). Transgenic approaches further confirm miRNAs, such as miR7695, miR398b, miR160a, and miR166k-166h (Campo et al, 2013;Li et al, 2014Li et al, , 2019Salvador-Guirao et al, 2018), positively regulate rice blast resistance; on the contrary, miR169a, miR164a, miR319b, miR396, and miR167d Wang et al, 2018;Zhang et al, 2018;Chandran et al, 2019;Zhao et al, 2019) act as negative regulators of rice immunity against the blast pathogen. miRNAs exert their biological functions via targeting mRNAs with sequence complementarity (Seitz, 2009); meanwhile, binding of miRNAs to their targets could be interfered with by endogenous noncoding RNAs, such as target mimics (Wu et al, 2013) and circular RNAs (circRNAs; Hansen et al, 2013).…”

“…miRNAs exert their biological functions via targeting mRNAs with sequence complementarity (Seitz, 2009); meanwhile, binding of miRNAs to their targets could be interfered with by endogenous noncoding RNAs, such as target mimics (Wu et al, 2013) and circular RNAs (circRNAs; Hansen et al, 2013). Target mimics have been reported to regulate rice immunity against the blast pathogen Chandran et al, 2019;Li et al, 2019), but it is unknown whether circRNAs are involved in the rice-M. oryzae interaction.…”