Expression profiles of genes regulated by BplMYB46 in Betula platyphylla

The transcription factor BplMYB46 has been identified as a regulator of abiotic stress responses and promoter of secondary wall deposition in Betula platyphylla.To investigate the downstream targets of BplMYB46,the expression profiles of genes in stems from BplMYB46-overexpressing(OE)and BplMYB46-silencing(SE)plants were studied.In OE stems,952 genes were upregulated,and 1469 were downregulated in comparison to SE stems.In a KEGG pathway enrichment analysis of differentially expressed genes(DEGs),1387 differentially expressed genes were annotated for 117 metabolic pathways.DEGs were abundant for metabolic pathway,secondary metabolite biosynthesis,plant hormone signal transduction,phenylpropanoid and flavonoid biosynthesis.DEGs were implicated lignin or cellulose biosynthesis,cell wall modification,xylem development,disease resistance,stress responses,and anthocyanin biosynthesis.These results suggested that BplMYB46 regulates cell wall development and stress resistance by affecting the expression of these genes.Our study further elucidates the mechanism by which BplMYB46 mediates abiotic stress responses and secondary cell wall biosynthesis in birch.

Identification of novel cis-elements bound by BplMYB46 involved in abiotic stress responses and secondary wall deposition

Transcription factors （TFs） play vital roles in various biological processes by binding to cis-acting elements to control expressions of their target genes. The MYB TF BplMYB46, from Betula platyphylla, is involved in abiotic stress responses and secondary wall deposition. In the present study, we used a TF-centered yeast onehybrid technology （TF-centered YIH） to identify the cis- acting elements bound by BplMYB46. We screened a shortinsert random library and identified three cis-elements bound by BplMYB46： an E-box （CA（A/T/C）（A/G/C）TG） and two novel motifs, a TO-box （T（GIA）TCG（C/G）） and a GT-box （A（G/T）T（AIC）GT（T/G）C）. Chromatin immunoprecipitation （CHIP） and effector-reporter coexpression assays inNicotiana tabacum confirmed binding of BplMYB46 to the TC-box, GT-box, and E-box motifs in the promoters of the phenylalanine ammonia lyase （PAL）, peroxidase （POD）, and superoxide dismutase （SOD） genes, which function in abiotic stress tolerance and secondary wall biosynthesis. This finding improves our understanding of potential regulatory mechanisms in the response to abiotic stress and secondary wall deposition of BplMYB46 in B. platyphylla.