Investigation of PtSGT1 and PtSGT4 Function in Cellulose Biosynthesis in Populus tomentosa Using CRISPR/Cas9 Technology.

Cellulose synthesis is a complex process in plant cells that is important for wood processing, pulping, and papermaking. Cellulose synthesis begins with the glycosylation of sitosterol by sitosterol glycosyltransferase (SGT) to produce sitosterol-glucoside (SG), which acts as the guiding primer for cellulose production. However, the biological functions of SGTs in Populus tomentosa(P. tomentosa) remain largely unknown. Two full-length PtSGT genes (PtSGT1 and PtSGT4) were previously isolated from P. tomentosa and characterized. In the present study, CRISPR/Cas9 gene-editing technology was used to construct PtSGT1-sgRNA and PtSGT4-sgRNA expression vectors, which were genetically transformed into P. tomentosa using the Agrobacterium-mediated method to obtain transgenic lines. Nucleic acid and amino acid sequencing analysis revealed both base insertions and deletions, in addition to reading frame shifts and early termination of translation in the transgenic lines. Sugar metabolism analysis indicated that sucrose and fructose were significantly downregulated in stems and leaves of mutant PtSGT1-1 and PtSGT4-1. Glucose levels did not change significantly in roots and stems of PtSGT1-1 mutants; however, glucose was significantly upregulated in stems and downregulated in leaves of the PtSGT4-1 mutants. Dissection of the plants revealed disordered and loosely arranged xylem cells in the PtSGT4-1 mutant, which were larger and thinner than those of the wild-type. This work will enhance our understanding of cellulose synthesis in the cell walls of woody plants.

A Novel Moderate Constitutive Promoter Derived from Poplar (Populus tomentosa Carrière).

A novel sequence that functions as a promoter element for moderate constitutive expression of transgenes, designated as the PtMCP promoter, was isolated from the woody perennial Populus tomentosa. The PtMCP promoter was fused to the GUS reporter gene to characterize its expression pattern in different species. In stable Arabidopsis transformants, transcripts of the GUS reporter gene could be detected by RT-PCR in the root, stem, leaf, flower and silique. Further histochemical and fluorometric GUS activity assays demonstrated that the promoter could direct transgene expression in all tissues and organs, including roots, stems, rosette leaves, cauline leaves and flowers of seedlings and maturing plants. Its constitutive expression pattern was similar to that of the CaMV35S promoter, but the level of GUS activity was significantly lower than in CaMV35S promoter::GUS plants. We also characterized the promoter through transient expression in transgenic tobacco and observed similar expression patterns. Histochemical GUS staining and quantitative analysis detected GUS activity in all tissues and organs of tobacco, including roots, stems, leaves, flower buds and flowers, but GUS activity in PtMCP promoter::GUS plants was significantly lower than in CaMV35S promoter::GUS plants. Our results suggested that the PtMCP promoter from poplar is a constitutive promoter with moderate activity and that its function is presumably conserved in different species. Therefore, the PtMCP promoter may provide a practical choice to direct moderate level constitutive expression of transgenes and could be a valuable new tool in plant genetic engineering.

Isolation of a LEAFY homolog from Populus tomentosa: expression of PtLFY in P. tomentosa floral buds and PtLFY-IR-mediated gene silencing in tobacco (Nicotiana tabacum).

To understand the genetic and molecular mechanisms underlying floral development in Populus tomentosa, we isolated PtLFY, a LEAFY homolog, from a P. tomentosa floral bud cDNA library. DNA gel blot analysis showed that PtLFY is present as a single copy in the genomes of both male and female individuals of P. tomentosa. The genomic copy is composed of three exons and two introns. Relative expression levels of PtLFY in tissues of P. tomentosa were estimated by RT-PCR; our results revealed that PtLFY mRNA is highly abundant in roots and both male and female floral buds. A low level of gene expression was detected in stems and vegetative buds, and no PtLFY-specific transcripts were detected in leaves. PtLFY expression patterns were analyzed during the development of both male and female floral buds in P. tomentosa via real-time quantitative RT-PCR. Continuous, stable and high-level expression of PtLFY-specific mRNA was detected in both male and female floral buds from September 13th to February 25th, but the level of PtLFY transcripts detected in male floral buds was considerably higher than in female floral buds. Our results also showed an inverted repeat PtLFY fragment (PtLFY-IR) effectively blocked flowering of transgenic tobacco plants, and that this effect appeared to be due to post-transcriptional silencing of the endogenous tobacco LFY homologs NFL1 and NFL2.

Characterization of the complete chloroplast genome of Calophaca sinica Rehd.

Calophaca sinica Rehd. is a tree species with high economic value, whose resource has been declining due to unreasonable exploitation. In this study, we sequenced, assembled, and annotated the complete chloroplast genome of C. sinica. The whole chloroplast genome size is 129,345 bp, it lacks an inverted repeat (IR) region. The GC content of the whole chloroplast genome is 34.51%. The chloroplast genome comprises 112 unique genes, including 77 protein-coding genes (PCGs), 30 transfer RNA (tRNA) genes, and 5 ribosomal RNA (rRNA) genes. Phylogenetic analyses of chloroplast genomes derived from 15 species indicated that C. sinica is close to Caragana and Tibetia species in Papilionoideae.

[Gene and gene engineering of carotenoid biosynthesis].

Carotenoids have a range of diverse biological functions and actions, especially playing an important role in human health with provitamin A activity, anti-cancer activity, enhancing immune ability and so on. Human body can't synthesis carotenoids by itself and must absorb them from outside. However, carotenoid contents in many plant are very low, and many kinds of carotenoid are difficult to produce by chemical ways. With the elucidation of carotenoid biosynthetic pathway and cloning genes of relative enzymes from microorganisms and higher plants, it is possible to regulate carotenoid biosynthesis via genetic engineering. This article reviews gene cloning of carotenoid biosynthetic enzymes in microorganisms and higher plants, and advances in the studies of carotenoid production in heterologous microorganisms and crop plants using gene-manipulated carotenoid biosynthesis.