Abstract
BackgroundE2 ubiquitin-conjugating (UBC) enzymes are an integral component of the ubiquitin proteasome system that play an important role in plant development, growth, and external stress responses. Several UBC genes have been identified in various plants. However, no studies exploring the functions of UBC genes in regulating fruit of strawberry have been reported. In the present study, a systematic analysis of the entire UBC family members were conducted in the genome of strawberry (Fragaria ×ananassa) based on bioinformatics method, and the gene functioning in strawberry ripening was explored.ResultsA total of 191 UBC genes were identified in the genome of cultivated strawberry. These genes were unevenly distributed across the 28 chromosomes from the 4 subgenomes of cultivated strawberry, ranging from 3 to 11 genes per chromosome. Moreover, the expansion of FaUBC genes in strawberry was mainly driven by WGD. All the FaUBC genes were clarified into 13 groups and most of them were included in the group VI. The gene structure analysis showed that the number of exons varied from 1 to 23, and the structure of genes had few differences within the same groups but a distinction in different groups. Identification of the cis-acting elements of the promoter revealed multiple regulatory elements that responded to plant growth and development, phytohormone responsive, and abiotic and biotic stress. Data from functional annotation indicated that FaUBC genes play a role in a variety of biological processes. The RNA-seq data showed that FaUBC genes displayed different expression pattern during the fruit ripening process and clarified into 6 clusters. In particular, cluster 3 exhibiting a sudden expression increase in the turning red stage were speculated to be involved in fruit ripening. Hence, two FaUBC genes (FaUBC76 and FaUBC78) were selected for gene function analysis by transient over-expression method. The results indicated that FaUBC76 has a positive effect on the fruit development and ripening in strawberry by up-regulating accumulation of anthocyanins. Moreover, expression of some maturity-related genes were also significantly increased, further supporting a role for FaUBC76 in the regulation of fruit ripening or softening. On the contrary, the overexpression of FaUBC78 significantly increased the firmness of strawberry fruit, indicating that FaUBC78 had a positive role in inhibiting the decrease of strawberry fruit firmness.ConclusionOur study not only provide comprehensive information on system evolution and function on UBC genes, but also give a new insight into explore the roles of FaUBC genes in the regulation of strawberry ripening.
Highlights
As a ubiquitous post-translational modification for eukaryotes, ubiquitination is involved in many cellular processes, including hormone signaling transduction [1], apoptosis [2], and biotic and abiotic stresses stresses [3]
In Arabidopsis, AtUBC32 is an endoplasmic reticulum-associated degradation (ERAD) component that functions in brassinosteroid-mediated salt stress tolerance [15]; AtUBC2 is implicated in repression of flowering [16]; AtUBC13 was involved in epidermal cell differentiation and iron deficiency responses [17, 18]
It was reported that the regulator RIN (Ripening-inhibitor) of tomato fruit ripening could directly combine with the E2 promoter region, and the fruit color was changed after silencing the E2 gene [6]
Summary
As a ubiquitous post-translational modification for eukaryotes, ubiquitination is involved in many cellular processes, including hormone signaling transduction [1], apoptosis [2], and biotic and abiotic stresses stresses [3]. Ubiquitinconjugating enzyme plays a crucial role in plant growth and development [6], and participates in environmental stresses [10, 11], immune response [12, 13], DNA damage and repair [14]. A tomato UBC13-type homologous protein, FNI3, is involved in the regulation of the immune response [19]. E2 ubiquitin-conjugating (UBC) enzymes are an integral component of the ubiquitin proteasome system that play an important role in plant development, growth, and external stress responses. No studies exploring the functions of UBC genes in regulating fruit of strawberry have been reported. A systematic analysis of the entire UBC family members were conducted in the genome of strawberry (Fragaria ×ananassa) based on bioinformatics method, and the gene functioning in strawberry ripening was explored
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