Large-scale rewiring of innate immunity circuitry and microRNA regulation during initial rice blast infection.

Rice blast is a recurrent fungal disease, and resistance to fungal infection is a complex trait. Therefore, a comprehensive examination of rice transcriptome and its variation during fungal infection is necessary to understand the complex gene regulatory networks. In this study, adopting Next-Generation Sequencing we profiled the transcriptomes and microRNAomes of rice varieties, one susceptible and the other resistant to M. oryzae, at multiple time points during the fungal infection. Our results revealed a substantial variation in the plant transcriptome and microRNAome as well as change to rice innate immunity during fungal infection. A number of putative R gene candidates were identified from a perturbed rice transcriptome analysis. The expression of genes and non-coding RNA molecules changed in both fungal resistant and susceptible plants during M. oryzae invasion discovered distinct pathways triggered in the susceptible and resistant plants. In addition, a number of fungus genes in the susceptible and resistant plants were constantly expressed at different time points, suggesting that they were likely to be the potential AVR genes. Our results revealed large-scale rewiring of innate immunity circuitry and microRNA regulation during initial rice blast infection, which would help to develop more robust blast-resistant rice plants.

Genome-wide screening and functional analysis identify a large number of long noncoding RNAs involved in the sexual reproduction of rice.

BACKGROUND: Long noncoding RNAs (lncRNAs) play important roles in a wide range of biological processes in mammals and plants. However, the systematic examination of lncRNAs in plants lags behind that in mammals. Recently, lncRNAs have been identified in Arabidopsis and wheat; however, no systematic screening of potential lncRNAs has been reported for the rice genome. RESULTS: In this study, we perform whole transcriptome strand-specific RNA sequencing (ssRNA-seq) of samples from rice anthers, pistils, and seeds 5 days after pollination and from shoots 14 days after germination. Using these data, together with 40 available rice RNA-seq datasets, we systematically analyze rice lncRNAs and definitively identify lncRNAs that are involved in the reproductive process. The results show that rice lncRNAs have some different characteristics compared to those of Arabidopsis and mammals and are expressed in a highly tissue-specific or stage-specific manner. We further verify the functions of a set of lncRNAs that are preferentially expressed in reproductive stages and identify several lncRNAs as competing endogenous RNAs (ceRNAs), which sequester miR160 or miR164 in a type of target mimicry. More importantly, one lncRNA, XLOC_057324, is demonstrated to play a role in panicle development and fertility. We also develop a source of rice lncRNA-associated insertional mutants. CONCLUSIONS: Genome-wide screening and functional analysis enabled the identification of a set of lncRNAs that are involved in the sexual reproduction of rice. The results also provide a source of lncRNAs and associated insertional mutants in rice.

Overexpression of microRNA OsmiR397 improves rice yield by increasing grain size and promoting panicle branching.

Increasing grain yields is a major focus of crop breeders around the world. Here we report that overexpression of the rice microRNA (miRNA) OsmiR397, which is naturally highly expressed in young panicles and grains, enlarges grain size and promotes panicle branching, leading to an increase in overall grain yield of up to 25% in a field trial. To our knowledge, no previous report has shown a positive regulatory role of miRNA in the control of plant seed size and grain yield. We determined that OsmiR397 increases grain yield by downregulating its target, OsLAC, whose product is a laccase-like protein that we found to be involved in the sensitivity of plants to brassinosteroids. As miR397 is highly conserved across different species, our results suggest that manipulating miR397 may be useful for increasing grain yield not only in rice but also in other cereal crops.