Abstract
Cucumber (Cucumis sativus L.) is an important vegetable crop worldwide and gibberellins (GAs) play important roles in the regulation of cucumber developmental and growth processes. GA oxidases (GAoxs), which are encoded by different gene subfamilies, are particularly important in regulating bioactive GA levels by catalyzing the later steps in the biosynthetic pathway. Although GAoxs are critical enzymes in GA synthesis pathway, little is known about GAox genes in cucumber, in particular about their evolutionary relationships, expression profiles and biological function. In this study, we identified 17 GAox genes in cucumber genome and classified them into five subfamilies based on a phylogenetic tree, gene structures, and conserved motifs. Synteny analysis indicated that the tandem duplication or segmental duplication events played a minor role in the expansion of cucumber GA2ox, GA3ox and GA7ox gene families. Comparative syntenic analysis combined with phylogenetic analysis provided deep insight into the phylogenetic relationships of CsGAox genes and suggested that protein homology CsGAox are closer to AtGAox than OsGAox. In addition, candidate transcription factors BBR/BPC (BARLEY B RECOMBINANT/BASIC PENTACYSTEINE) and GRAS (GIBBERELLIC ACID-INSENSITIVE, REPRESSOR of GAI, and SCARECROW) which may directly bind promoters of CsGAox genes were predicted. Expression profiles derived from transcriptome data indicated that some CsGAox genes, especially CsGA20ox1, are highly expressed in seedling roots and were down-regulated under GA3 treatment. Ectopic over-expression of CsGA20ox1 in Arabidopsis significantly increased primary root length and lateral root number. Taken together, comprehensive analysis of CsGAoxs would provide a basis for understanding the evolution and function of the CsGAox family.
Highlights
Gibberellins (GAs), a large group of tetracyclic diterpenes, control diverse aspects of plant growth and development throughout the life cycle of plants, including seed germination [1], stem elongation [2,3], leaf expansion [4], alteration of sex expression [5,6,7], flower and root development [8,9,10] and fruit set and development [11,12]
To identify GA oxidases (GAoxs) family genes in cucumber genome, the 16 Arabidopsis GAox proteins and the consensus protein sequences of 2OG-FeII_Oxy (PF03171) and DIOX_N (PF14226) were employed as a query to search against the cucumber genome database using the BlastP program
A total of 21 proteins in the cucumber genome were identified as possible members of the CsGAox family (Figure S1)
Summary
Gibberellins (GAs), a large group of tetracyclic diterpenes, control diverse aspects of plant growth and development throughout the life cycle of plants, including seed germination [1], stem elongation [2,3], leaf expansion [4], alteration of sex expression [5,6,7], flower and root development [8,9,10] and fruit set and development [11,12]. 136 naturally occurring GAs have been discovered [13], most of these molecules have been identified as non-bioactive GAs in plants, and these act as precursors for the bioactive forms or are de-activated metabolites [14]. The first stage, which is catalyzed by soluble enzymes and occurs in plastids, leads to the synthesis of the tetracyclic hydrocarbon and entkaurene. The final stage of the pathway, which has been identified as primarily responsible for the regulation of bioactive GA synthesis, is catalyzed by two GA oxidases (GAoxs) known as GA 20-oxidase (GA20ox) and GA 3-oxidase (GA3ox) in the cytosol of the cell [17,18]. In the pathways and regulation of GA degradation, bioactive GAs or their immediate precursors are inactivated by the third family of GAoxs, the GA 2-oxidases (GA2oxs), including C19-GA2oxs and C20-GA2oxs [14,19]
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