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Abstract
Short tandem target mimic (STTM), which is composed of two short sequences mimicking small RNA target sites, separated by a linker of optimal size, can block the functions of all members in a miRNA family. microRNA393 (miR393), which is one of the conserved miRNA families in plants, can regulate plant root growth, leaf development, plant architecture, and stress resistance. In order to verify the role of miR393 in the secondary growth of trees, we created its STTM transgenic poplar lines (STTM393). The expression of miR393 in STTM393 lines was reduced by over 10 times compared with the control plants. STTM393 lines showed promoted growth with about 20% higher, 15% thicker, and 2–4 more internodes than the control plants after 3 months of growth. The cross-section of the stems showed that STTM393 lines had wider phloem, xylem, and more cambium cell layers than control plants, and the lignin content in STTM393 lines was also higher as revealed by staining and chemical determination. Based on the transcriptome analysis, the genes related to the auxin signaling pathway, cell cyclin, cell expansion, and lignin synthesis had higher expression in STTM393 lines than that in control plants. The higher expression levels of FBL family members suggested that the auxin signaling pathway was strengthened in STTM393 lines to promote plant growth. Therefore, the knockdown of miR393 using the STTM approach provides a way to improve poplar growth and biomass production.
Highlights
Poplar is one of the important carbon-neutral biomass for the production of timber products, paper pulping, chemicals, and biofuels (Gui et al, 2020)
We obtained 30 STTM393 transgenic lines by Agrobacteriummediated leaf disk method, and qRT-PCR showed that the expression of miR393 in 13 randomly selected lines was reduced over 10 times (Supplementary Figure 1)
Three STTM393 lines (i.e., STTM393-2, STTM393-8, and STTM393-16) with obvious phenotypic changes were used for further analysis
Summary
Poplar is one of the important carbon-neutral biomass for the production of timber products, paper pulping, chemicals, and biofuels (Gui et al, 2020). In order to understand miRNA functions, the major approaches were used by generating the transgenic lines in which the genes that encode miRNAs or the target gene of miRNAs were overexpressed (Zhu et al, 2009; Zhang et al, 2010; Curaba et al, 2013). These approaches were insufficient to fully understand miRNA functions. MiRNAs tend to be gene families, and previous approaches could generally overexpress only one member at a time (Sieber et al, 2007; Curaba et al, 2013)
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