Circular RNAs (circRNAs), a class of recently discovered non-coding RNAs, play a role in biological and developmental processes. A recent study showed that circRNAs exist in plants and play a role in their environmental stress responses. However, cotton circRNAs and their role in Verticillium wilt response have not been identified up to now. In this study, two CSSLs (chromosome segment substitution lines) of G.barbadense introgressed into G. hirsutum, CSSL-1 and CSSL-4 (a resistant line and a susceptible line to Verticillium wilt, respectively), were inoculated with V. dahliae for RNA-seq library construction and circRNA analysis. A total of 686 novel circRNAs were identified. CSSL-1 and CSSL-4 had similar numbers of circRNAs and shared many circRNAs in common. However, CSSL-4 differentially expressed approximately twice as many circRNAs as CSSL-1, and the differential expression levels of the common circRNAs were generally higher in CSSL-1 than in CSSL-4. Moreover, two C-RRI comparisons, C-RRI-vs-C-RRM and C-RRI-vs-C-RSI, possessed a large proportion (approximately 50%) of the commonly and differentially expressed circRNAs. These results indicate that the differentially expressed circRNAs may play roles in the Verticillium wilt response in cotton. A total of 280 differentially expressed circRNAs were identified. A Gene Ontology analysis showed that most of the ‘stimulus response’ term source genes were NBS family genes, of which most were the source genes from the differentially expressed circRNAs, indicating that NBS genes may play a role in Verticillium wilt resistance and might be regulated by circRNAs in the disease-resistance process in cotton.

The AP2/ERF superfamily of transcription factors is one of the largest transcription factor families in plants and plays an important role in plant development processes and stress responses. In this study, BjABR1, an AP2/ERF superfamily gene, from tuber mustard (Brassica juncea var. tumida Tsen et Lee), sharing high amino acid sequence similarity with the AtABR1 (Arabidopsis thaliana AP2-like abscisic acid repressor 1) gene, were performed functional research, and the ABR1 homologous genes in Brassica species were identified and performed phylogenetic analysis. The promoter sequence of BjABR1 contained many phytohormone- and stress-related cis-elements; ABA (abscisic acid) and abiotic stresses can induce BjABR1 expression in tuber mustard; overexpression of BjABR1 in Arabidopsis can alleviate plant sensitivity to ABA and salt and osmotic stresses, and the alleviation may be due to changes in stress/ABA-induced gene expression. These results indicated that BjABR1 functions in ABA and abiotic stress responses. By BLAST searches against the genome database of five Brassica species (three diploids, B. rapa, B. nigra, and B. oleracea, and two allotetraploid, B. juncea and B. napus) using the protein sequence of AtABR1, 3, 3, 3, 6, and 5 ABR1 homologous genes in B. nigra, B. rapa, B. oleracea, B. juncea, and B. napus were identified, respectively, and they shared high sequence similarity. By sequence analysis, annotation mistakes of the protein-coding regions of two ABR1 homologous genes, GSBRNA2T00134741001 and BjuB007684, were found and corrected. Then, the evolution analysis of these ABR1 homologous genes showed that the ancestor of the three diploid species had three ABR1 homologous genes and each diploid inherited all the three genes from their ancestor; then, allotetraploid B. juncea inherited all the six genes from B. rapa and B. nigra with no gene lost, while allotetraploid B. napus inherited all the three genes from B. oleracea and two genes from B. rapa with one gene lost, indicating that ABR1 homologous genes possessed greater hereditary conservation in Brassica species. The ABR1 homologous genes between B. rapa and B. oleracea shared much higher sequence similarity compared to that of B. nigra in diploid species, indicating that ABR1 homologous genes in B. nigra had experienced more rapid evolution, and B. rapa and B. oleracea may share closer relationship compared to B. nigra. Moreover, the spatial and temporal expression analysis of six ABR1 homologous genes of tuber mustard showed that they possessed different expression models. These results imply that ABR1 homologous genes are important to Brassica plants, and they may possess similar function in ABA and abiotic stress responses but play a role in different tissues and growing stages of plant. This study will provide the foundation to the functional research of ABR1 homologous genes in the Brassica species and help to reveal and understand the evolution mechanisms of Brassica species.