Abstract
Flowering connects vegetative and generative developmental phases and plays a significant role in strawberry production. The mechanisms that regulate strawberry flowering time are unclear. B-box transcription factors (BBXs) play important roles in the flowering time regulation of plants. Nevertheless, BBXs in octoploid cultivated strawberry (Fragaria ananassa) and their functions in flowering time regulation have not been identified. Here, we identified 51 FaBBXs from cultivated strawberry and 16 FvBBXs from diploid wild strawberry (Fragaria vesca), which were classified into five groups according to phylogenetic analysis. Further evolutionary analysis showed that whole-genome duplication or segmental duplication is a crucial factor that leads to the expansion of the BBX gene family in two strawberry species. Moreover, some loss and acquisition events of FaBBX genes were identified in the genome of cultivated strawberry that could have affected traits of agronomic interest, such as fruit quality. The promoters of FaBBX genes showed an enrichment in light-responsive, cis-regulatory elements, with 16 of these genes showing changes in their transcriptional activity in response to blue light treatment. On the other hand, FaBBX28c1, whose transcriptional activity is reduced in response to blue light, showed a delay in flowering time in Arabidopsis transgenic lines, suggesting its role in the regulation of flowering time in cultivated strawberry. Our results provide new evolutionary insight into the BBX gene family in cultivated strawberry and clues regarding their function in flowering time regulation in plants.
Highlights
Transcription factors play key roles in various plant biological processes, such as stress responses, development regulation, and secondary metabolic pathway mediation.A genome-wide identification of transcription factors in Arabidopsis shows that a large class of 1500 transcription factors is encoded by the genome, approximately 45% of which are specific to plants [1]
Our results show a downregulation of those genes in the overexpression lines, which suggests that FaBBX28c1 may function as an upstream negative regulator of the pathway (Figure 13), which is similar to its homologs in Arabidopsis [6]
Evolutionary analysis shows that large-scale duplication events are the main force driving the expansion of the B-box proteins (BBXs) gene family in strawberry
Summary
Transcription factors play key roles in various plant biological processes, such as stress responses, development regulation, and secondary metabolic pathway mediation.A genome-wide identification of transcription factors in Arabidopsis shows that a large class of 1500 transcription factors is encoded by the genome, approximately 45% of which are specific to plants [1]. -called B-box proteins (BBXs) are a class of zinc finger transcription factors that contain one or two B-box conserved domains mediating protein–protein interactions [2]. Systematic identification of the BBX family in Arabidopsis has identified 32 AtBBXs (AtBBX1-AtBBX32) that can be further classified into 5 groups (Group I–Group V) on the basis of the presence of domains [3]. I contain two B-box domains in tandem and a CCT (CONSTANS, CO-like, and TOC1). Structure Group II members are similar to Group I, both of which contain two tandem B-box domains and one CCT domain; differences in their second B-box domains were observed. The AtBBX members of structure Group III contain a single B-box domain in association with a CCT domain. Structure Group IV contains two B-boxes, and no CCT domain is found. Structure Group V consists of members with only a single
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