Pestalotiopsis Species Associated with Blueberry Leaf Spots and Stem Cankers in Sichuan Province of China.

Blueberry leaf spots and stem cankers caused by Pestalotiopsis spp. have become a serious threat for the production of blueberry in Sichuan Province. To characterize the etiology of the diseases connected with these fungi, samples showing leaf spot and stem canker symptoms were collected from the 12 main blueberry-growing areas of Sichuan Province from 2015 to 2020 and used for pathogen isolation. In total, 91 fungal isolates were obtained with preliminary morphological identification and 48 representative strains were selected for further pathogenicity test and molecular identification. Four species, including Pestalotiopsis clavispora (Neopestalotiopsis clavispora) (57.14%), P. trachicarpicola (28.57%), P. chamaeropis (13.19%), and P. adusta (1.10%), were identified based on conidial morphology, cultural characteristics, and phylogenetic analysis of the internal transcribed spacer region, partial sequence of the ß-tubulin gene, and the translation elongation factor 1-α. Pathogenicity tests showed that four species were pathogenic to leaves and stems of blueberry. Among them, P. clavispora (N. clavispora) was the most aggressive as the predominant species to cause both leaf spot and stem canker. P. trachicarpicola and P. chamaeropis were mainly isolated from leaves but also pathogenic to stems. P. adusta was only isolated from stems but also pathogenic to leaves. To the best of our knowledge, this is the first report of P. chamaeropis and P. adusta as pathogens causing leaf spots and stem canker on blueberry. The results provide helpful information in disease diagnosis and management of blueberry.

circRNAs Are Involved in the Rice-Magnaporthe oryzae Interaction.

Circular RNAs (circRNAs) play roles in various biological processes, but their functions in the rice (Oryza sativa) response to Magnaporthe oryzae remain elusive. Here, we demonstrate that circRNAs are involved in the rice-M. oryzae interaction using comparative circRNA-sequencing and transgenic approaches. We identified 2932 high-confidence circRNAs from young leaves of the blast-resistant accession International Rice Blast Line Pyricularia-Kanto51-m-Tsuyuake (IR25) and the blast-susceptible accession Lijiangxin Tuan Heigu (LTH) under M oryzae-infected or uninfected conditions; 636 were detected specifically upon M oryzae infection. The circRNAs in IR25 were significantly more diverse than those in LTH, especially under M. oryzae infection. Particularly, the number of circRNAs generated per parent gene was much higher in IR25 than in LTH and increased in IR25 but decreased in LTH upon M. oryzae infection. The higher diversity of circRNAs in IR25 was further associated with more frequent 3' and 5' alternative back-splicing and usage of complex splice sites. Moreover, a subset of circRNAs was differentially responsive to M oryzae in IR25 and LTH. We further confirmed that circR5g05160 promotes rice immunity against M oryzae Therefore, our data indicate that circRNA diversity is associated with different responses to M oryzae infection in rice and provide a starting point to investigate a new layer of regulation in the rice-M oryzae interaction.

Osa-miR1873 fine-tunes rice immunity against Magnaporthe oryzae and yield traits.

MicroRNAs (miRNAs) are known to fine-tune growth, development, and stress-induced responses. Osa-miR1873 is a rice-specific miRNA targeting LOC_Os05g01790. Here, we show that Osa-miR1873 fine-tunes rice immunity against Magnaporthe oryzae and yield traits via LOC_Os05g01790. Osa-miR1873 was significantly upregulated in a susceptible accession but downregulated in a resistance accession at 24 h post-inoculation (hpi) of M. oryzae. Overexpressing Osa-miR1873 enhanced susceptibility to M. oryzae and compromised induction of defense responses. In contrast, blocking Osa-miR1873 through target mimicry compromised susceptibility to M. oryzae and enhanced induction of defense responses. Altered expression of Osa-miR1873 also resulted in some defects in yield traits, including grain numbers and seed setting rate. Moreover, overexpression of the target gene LOC_Os05g01790 increased rice blast disease resistance but severely penalized growth and yield. Taken together, we demonstrate that Osa-miR1873 fine-tunes the rice immunity-growth trade-off via LOC_Os05g01790, and blocking Osa-miR1873 could improve blast disease resistance without significant yield penalty. Thus, the Osa-miR1873-LOC_Os05g01790 regulatory module is valuable in balancing yield traits and blast resistance.

Suppression of rice miR168 improves yield, flowering time and immunity.

MicroRNA168 (miR168) is a key miRNA that targets Argonaute1 (AGO1), a major component of the RNA-induced silencing complex1,2. Previously, we reported that miR168 expression was responsive to infection by Magnaporthe oryzae, the causal agent of rice blast disease3. However, how miR168 regulates immunity to rice blast and whether it affects rice development remains unclear. Here, we report our discovery that the suppression of miR168 by a target mimic (MIM168) not only improves grain yield and shortens flowering time in rice but also enhances immunity to M. oryzae. These results were validated through repeated tests in rice fields in the absence and presence of rice blast pressure. We found that the miR168-AGO1 module regulates miR535 to improve yield by increasing panicle number, miR164 to reduce flowering time, and miR1320 and miR164 to enhance immunity. Our discovery demonstrates that changes in a single miRNA enhance the expression of multiple agronomically important traits.

Osa-miR162a fine-tunes rice resistance to Magnaporthe oryzae and Yield.

MicroRNAs (miRNAs) play essential roles in rice immunity against Magnaporthe oryzae, the causative agent of rice blast disease. Here we demonstrate that Osa-miR162a fine-tunes rice immunity against M. oryzae and yield traits. Overexpression of Osa-miR162a enhances rice resistance to M. oryzae accompanying enhanced induction of defense-related genes and accumulation of hydrogen peroxide (H2O2). In contrast, blocking Osa-miR162 by overexpressing a target mimic of Osa-miR162a enhances susceptibility to blast fungus associating with compromised induction of defense-related gene expression and H2O2 accumulation. Moreover, the transgenic lines overexpressing Osa-miR162a display decreased seed setting rate resulting in slight reduced yield per plant, whereas the transgenic lines blocking Osa-miR162 show an increased number of grains per panicle, resulting in increased yield per plant. Altered accumulation of Osa-miR162 had a limited impact on the expression of rice Dicer-like 1 (OsDCL1) in these transgenic lines showing normal gross morphology, and silencing of OsDCL1 led to enhanced resistance to blast fungus similar to that caused by overexpression of Osa-miR162a, suggesting the involvement of OsDCL1 in Osa-miR162a-regulated resistance. Together, our results indicate that Osa-miR162a is involved in rice immunity against M. oryzae and fine-tunes resistance and yield.

Expressing a Target Mimic of miR156fhl-3p Enhances Rice Blast Disease Resistance Without Yield Penalty by Improving SPL14 Expression.

MicroRNAs (miRNAs) play essential roles in the regulation of plant growth and defense responses. More and more, miRNA-3ps are reported to act in plant development and immunity. miR156 is a conserved miRNA, and most previous studies focus on its roles in plant growth, development, and yield determinacy. Here, we show that expressing a target mimic of miR156fhl-3p led to enhanced rice blast disease resistance without a yield penalty. miR156fhl-3p was differentially responsive to Magnaporthe oryzae in susceptible and resistant accessions. Transgenic lines expressing a target mimic of miR156fhl-3p (MIM156-3p) exhibited enhanced rice blast disease resistance and increased expression of defense-related genes. MIM156-3p also enhanced the mRNA abundance of SPL14 and WRKY45 by down-regulating miR156-5p and pre-miR156. Moreover, MIM156-3p lines displayed a decreased number of second rachis branches per panicle but enlarged grains, leading to unchanged yield per plant. Consistently, overexpressing miR156h (OX156) led to enhanced susceptibility to M. oryzae and decreased the expression of SPL14 and WRKY45. Our results indicate that miR156fhl-3p mounts a regulatory role on miR156-5p, which subsequently regulates the expression of SPL14 and WRKY45 to improve rice blast disease resistance.