Background APETALA2 -like genes encode plant-specific transcription factors, some of which possess one microRNA172 (miR172) binding site. The miR172 and its target euAP2 genes are involved in the process of phase transformation and flower organ development in many plants. However, the roles of miR172 and its target AP2 genes remain largely unknown in Brassica napus ( B. napus ). Results In this study, 19 euAP2 and four miR172 genes were identified in the B. napus genome. A sequence analysis suggested that 17 euAP2 genes were targeted by Bna-miR172 in the 3′ coding region. EuAP2 s were classified into five major groups in B.napus . This classification was consistent with the exon-intron structure and motif organization. An analysis of the nonsynonymous and synonymous substitution rates revealed that the euAP2 genes had gone through purifying selection. Whole genome duplication (WGD) or segmental duplication events played a major role in the expansion of the euAP2 gene family. A cis-regulatory element (CRE) analysis suggested that the euAP2 s were involved in the response to light, hormones, stress, and developmental processes including circadian control, endosperm and meristem expression. Expression analysis of the miR172-targeted euAP2s in nine different tissues showed diverse spatiotemporal expression patterns. Most euAP2 genes were highly expressed in the floral organs, suggesting their specific functions in flower development. BnaAP2–1 , BnaAP2–5 and BnaTOE1–2 had higher expression levels in late-flowering material than early-flowering material based on RNA-seq and qRT-PCR, indicating that they may act as floral suppressors. Conclusions Overall, analyses of the evolution, structure, tissue specificity and expression of the euAP2 genes were peformed in B.napus . Based on the RNA-seq and experimental data, euAP2 may be involved in flower development. Three euAP2 genes ( BnaAP2–1 , BnaAP2–5 and BnaTOE1–2 ) might be regarded as floral suppressors. The results of this study provide insights for further functional characterization of the miR172 / euAP2 module in B.napus . Electronic supplementary material The online version of this article (10.1186/s12870-019-1936-2) contains supplementary material, which is a...

Lignin is an important biological polymer in plants that is necessary for plant secondary cell wall ontogenesis. The laccase (LAC) gene family catalyzes lignification and has been suggested to play a vital role in the plant kingdom. In this study, we identified 45 LAC genes from the Brassica napus genome (BnLACs), 25 LAC genes from the Brassica rapa genome (BrLACs) and 8 LAC genes from the Brassica oleracea genome (BoLACs). These LAC genes could be divided into five groups in a cladogram and members in same group had similar structures and conserved motifs. All BnLACs contained hormone- and stress- related elements determined by cis-element analysis. The expression of BnLACs was relatively higher in the root, seed coat and stem than in other tissues. Furthermore, BnLAC4 and its predicted downstream genes showed earlier expression in the silique pericarps of short silique lines than long silique lines. Three miRNAs (miR397a, miR397b and miR6034) target 11 BnLACs were also predicted. The expression changes of BnLACs under series of stresses were further investigated by RNA sequencing (RNA-seq) and quantitative real-time polymerase chain reaction (qRT-PCR). The study will give a deeper understanding of the LAC gene family evolution and functions in B. napus.

Rapeseed (Brassica napus L.) is the second most important oilseed crop in edible vegetable oil and bioenergy; however, drought stress generally causes a decrease in rapeseed yield and oil content, especially during the reproductive stage. In our study, we measured the oil and protein contents and gibberellic acid (GA) and abscisic acid (ABA) levels in seeds that were acquired on the 30th, 40th, and 50th days after flowering under control and drought treatments. RNA and protein libraries were constructed from the stressed seeds to perform transcriptome and proteome analyses, respectively. Our results demonstrated that the oil content decreased due to four primary mechanisms: downregulation of fatty acid biosynthesis‐associated genes and proteins; upregulation of fatty acid degradation‐associated genes and proteins; enhancement of protein storage due to changes in the abundances of relevant genes and proteins; and upregulation of Gly‐Asp‐Ser‐Leu (GDSL) gene expression, potentially as the result of upregulating the GA biosynthesis gene GA20ox3 and downregulating the GA inactivating gene GA2ox3 and thus an increase in GA content. During seed maturation, oil storage change may also relate to increasing ABA content as the upregulation of two members of NCED6 (9‐cis‐epoxycarotenoid dioxygenase) gene family involved in ABA biosynthesis, and the upregulation of genes involved in ABA signal transduction. These results will help to establish a foundation for breeding excellent varieties of rapeseed with high oil content for areas with frequent droughts to promote the supply of edible vegetable oil and biofuel.

Background Leaf color mutants have reduced photosynthetic efficiency, which has severely negative impacts on crop growth and economic product yield. There are different chlorophyll mutants in Arabidopsis and crops that can be used for genetic control and molecular mechanism studies of chlorophyll biosynthesis, chloroplast development and photoefficiency. Chlorophyll mutants in Brassica napus are mostly used for mapping and location research but are rarely used for physiological research. The chlorophyll-deficient mutant in this experiment were both genetically mapped and physiologically analyzed. Results In this study, yellow leaf mutant of Brassica napus L. mutated by ethyl methyl sulfone (EMS) had significantly lower chlorophyll a, b and carotenoid contents than the wild type, and the net photosynthetic efficiency, stomatal conductance and transpiration rate were all significantly reduced. The mutant had sparse chloroplast distribution and weak autofluorescence. The granule stacks were reduced, and the shape was extremely irregular, with more broken stromal lamella. Transcriptome data analysis enriched the differentially expressed genes mainly in phenylpropane and sugar metabolism. The mutant was mapped to a 2.72 Mb region on A01 by using BSA-Seq, and the region was validated by SSR markers. Conclusions The mutant chlorophyll content and photosynthetic efficiency were significantly reduced compared with those of the wild type. Abnormal chloroplasts and thylakoids less connected to the stroma lamella appeared in the mutant. This work on the mutant will facilitate the process of cloning the BnaA01.cd gene and provide more genetic and physiological information concerning chloroplast development in Brassica napus.

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