Abstract
Digital gene expression profiling technology was used to examine the changes in gene expression during floral transition in pak choi. A total of 1486 differentially expressed genes (DEGs) during floral transition were identified, of which 505 were upregulated and 981 were downregulated. Gene ontology enrichment analysis showed that the proteins encoded by DEGs were mainly located in eight cell regions including the apoplast, plant-type cell wall, chloroplast, etc. They had eight kinds of molecular functions such as transcription factor and oxidoreductase, and involved in 72 biological processes containing jasmonic acid and salicylic acid metabolism, glucose metabolism, the MAPK cascade, etc. Further pathway enrichment analysis showed that four metabolic pathways were significantly enriched by DEGs. DEGs that exhibited at least a 10-fold difference were analyzed in detail. Results showed that flavonoid metabolism and phenylpropanoid biosynthesis (or pathways) were significantly enriched and the corresponding gene number was the highest. Moreover, 15 genes among the highly expressed genes were involved in reproductive development, of which five homologues in Arabidopsis thaliana were directly related to floral transition, which were predicted to have a similar function in pak choi.
Highlights
The transition from vegetative growth to reproductive growth is relevant in the perpetuation of species, and related closely to human life; this transition in higher plants is regulated by endogenous and exogenous signals [1,2,3]
The differentially expressed genes (DEGs) with expression of 30-fold or greater accounted for only 1.08%, of which only 2 were upregulated and 14 were downregulated at stage 1. These results showed that the number of DEGs with significant difference was low, and it significantly decreased with differences increasing during floral transition in pak choi
These findings indicated that the homologues of Bra022565, Bra034674, Bra027530, Bra003998, and Bra031255 in A. thaliana were directly related to floral transition, which predicted that these genes may have similar functions in pak choi and need to be investigated further
Summary
The transition from vegetative growth to reproductive growth is relevant in the perpetuation of species, and related closely to human life; this transition in higher plants is regulated by endogenous and exogenous signals [1,2,3]. With the completion of whole genome sequencing in the model plants Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), the molecular mechanisms of flowering were investigated, and this endeavour has achieved significant progress [4]. The recent completion of whole genome sequencing and the constant enrichment of information on gene annotation in Chinese cabbage, which is the representative of the Brassica species [10,11], facilitates the gene comparison and screening for expression profile analysis of pak choi and provides an opportunity for genetic improvement and molecular design breeding among Brassica species. Some studies on flower molecular regulation in Brassica species have been conducted [12,13,14,15,16], information is still lacking compared with the flowering molecular mechanism of the model plant A. thaliana. Further studies on the flowering mechanism of pak choi are necessary in B. rapa, as well as in breeding within Brassicaceae
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