Circular RNAs are widely existing in eukaryotes. However, there is as yet no tissue-specific Arabidopsis circular RNA database, which hinders the study of circular RNA in plants. Here, we used 622 Arabidopsis RNA sequencing data sets from 87 independent studies hosted at NCBI SRA and developed AtCircDB to systematically identify, store and retrieve circular RNAs. By analyzing back-splicing sites, we characterized 84 685 circular RNAs, 30 648 tissue-specific circular RNAs and 3486 microRNA–circular RNA interactions. In addition, we used a metric (detection score) to measure the detection ability of the circular RNAs using a big-data approach. By experimental validation, we demonstrate that this metric improves the accuracy of the detection algorithm. We also defined the regions hosting enriched circular RNAs as super circular RNA regions. The results suggest that these regions are highly related to alternative splicing and chloroplast. Finally, we developed a comprehensive tissue-specific database (AtCircDB) to help the community store, retrieve, visualize and download Arabidopsis circular RNAs. This database will greatly expand our understanding of circular RNAs and their related regulatory networks. AtCircDB is freely available at http://genome.sdau.edu.cn/circRNA.

Circular RNA (circRNAs) may mediate mRNA expression as miRNA sponge. Since the community has paid more attention on circRNAs, a lot of circRNA databases have been developed for plant. However, a comprehensive collection of circRNAs in crop response to abiotic stress is still lacking. In this work, we applied a big-data approach to take full advantage of large-scale sequencing data, and developed a rich circRNA resource: CropCircDB for maize and rice, later extending to incorporate more crop species. We also designed a metric: stress detections score, which is specifically for detecting circRNAs under stress condition. In summary, we systematically investigated 244 and 288 RNA-Seq samples for maize and rice, respectively, and found 38 785 circRNAs in maize, and 63 048 circRNAs in rice. This resource not only supports user-friendly JBrowser to visualize genome easily, but also provides elegant view of circRNA structures and dynamic profiles of circRNA expression in all samples. Together, this database will host all predicted and validated crop circRNAs response to abiotic stress.

Phosphorylation can quickly switch on/off protein functions. Here, we reported pre-mRNA processing 4 kinase A (PRP4KA), and its paralogs interact with Serrate (SE), a key factor in RNA processing. PRP4KA phosphorylates at least five residues of SE in vitro and in vivo. Hypophosphorylated, but not hyperphosphorylated, SE variants could readily rescue se phenotypes in vivo. Moreover, hypophosphorylated SE variants had stronger binding affinity to microprocessor component HYL1 and were more resistant to degradation by 20 S proteasome than hyperphosphorylated counterparts. Knockdown of the kinases enhanced the accumulation of hypophosphorylated SE. However, the excessive SE interfered with the assembly and function of SE-scaffolded macromolecule complexes, causing the se -like defects in the mutant and wild-type backgrounds. Thus, phosphorylation of SE via PRP4KA can quickly clear accumulated SE to secure its proper amount. This study provides new insight into how protein phosphorylation regulates miRNA metabolism through controlling homeostasis of SE accumulation in plants.