Background: The B3 superfamily (B3s) represents a class of large plant-specific transcription factors, which play diverse roles in plant growth and development process including flowering induction. However, identification and functional surveys of B3 superfamily have not been reported in ethylene-induced pineapple flowering (Ananas comosus). Results: 57 B3 genes containing B3 domain were identified and phylogenetically classified into five subfamilies. Chromosomal localization analysis revealed that 54 of 57 AcB3s were located on 21 Linkage Groups (LG). Collinearity analysis demonstrated that the segmental duplication was the main event in the evolution of B3 gene superfamily, and most of them were under purifying selection. The analysis of cis-element composition suggested that most of these genes may have function in response to abscisic acid, ethylene, MeJA, light, and abiotic stress. qRT-PCR analysis of 40 AcB3s containing ethylene responsive elements exhibited that the expression levels of 35 genes were up-regulated within 1 d after ethephon treatment and some were highly expressed in flower bud differentiation period in stem apex, such as Aco012003, Aco019552 and Aco014401. Conclusion: This study provides a basic information of AcB3s and clues for involvement of some AcB3s in ethylene-induced flowering in pineapple.

Hylocereus polyrhizus Britt. & Rose (Cactaceae), commonly known as pitaya or dragon fruit, is widely cultured in tropical and subtropical regions of China and has become increasingly important fruit in recent years. In October 2014, in a survey of diseases on pitaya, approximately 44% of field plants showing virus-like symptoms including chlorotic halos and small chlorotic spots on stems were observed in Qionghai City of Hainan Island, China. Flexuous filamentous virus particles of about 600 nm in length were observed from stem-sap preparation of four symptomatic plants with a transmission electron microscope (TEM) (see Supplementary Fig. 1). To further ascertain the presence of Cactus virus X (CVX), stems from 20 symptomatic samples (including 4 samples found positive by TEM) and 20 healthy samples were collected from different fields for RT-PCR. Total RNAs were extracted and reverse transcribed into using random primers according to the manufacturer's instructions for the RevertAid first strand cDNA syn...

The B3 superfamily is a plant-specific family, which involves in growth and development process. By now, the identification of B3 superfamily in pineapple ( Ananas comosus ) has not reported. In this study, 57 B3 genes were identified and further phylogenetically classified into five subfamilies, all genes contained B3 domain. Chromosomal localization analysis revealed that 54 of 57 AcB3 genes were located on 21 chromosomes.Collinearity analysis indicated that the segmental duplication was the main event in the evolution of B3 gene superfamily and most of them were under purifying selection. Moreover, there were 7 and 39 pairs of orthologous B3s were identified between pineapple and Arabidopsis or rice, respectively, which indicated the closer genetic relationship between pineapple and rice. Most genes had cis -element of abscisic acid, ethylene, MeJA, light, and abiotic stress. qRT-PCR showed that the expression level of most AcB3 genes were up-regulated within 1 d after ethephon treatment and expressed high level in flower bud differentiation period in stem apex. This study provide a comprehensive understanding of AcB3s and a basis for future molecular studies of ethephon induced pineapple flowering.