Huaming An

Z. armatum is an economically valued crop known for its rich aroma and medicinal properties. This study identified 45 members of the SQUAMOSA-PROMOTER BINDING PROTEIN LIKE (SPL) gene family in the genome of Z. armatum. Phylogenetic and collinearity analyzes demonstrated a close relationship between ZaSPLs and ZbSPLs from B subgenomes of Zanthoxylum bungeanum. Our miRNA sequencing revealed a high degree of conservation of miR156a within Z. armatum, with the za-miR156a sequence identical to miR156-5p in Arabidopsis thaliana and Citrus sinensis. Of the 45 genes identified by ZaSPLs, 21 were targeted by za-miR156a, transient co-expression experiments in N. benthamiana demonstrated the targeting relationship between za-miR156 and ZaSPL21. Furthermore, RNA-seq and qRT-PCR analysis revealed that ZaSPL genes exhibited elevated expression levels in juvenile tissues of Z. armatum. The expression of nine representative ZaSPL genes were upregulated under polyethylene glycol (PEG) and abscisic acid (ABA). Overexpression of ZaSPL21 delayed the germination of transgenic tobacco and facilitated the flowering process in transgenic N. benthamiana. Significant up-regulation in the expression levels of flowering-related genes such as NbFT1, NbPIP2;1, NbTCP1, NbCOL1, NbGI2, NbGAI1, NbCKX2, and NbARR4 was observed in transgenic plants, suggesting that ZaSPL21 may stimulate plant flowering by regulation of these genes. Furthermore, ZaSPL21 also increased the germination speed of transgenic tobacco seeds during drought and salt stress conditions, and improved the salt tolerance of transgenic seedlings. In conclusion, our study contributes to understanding the functional analysis of the SPL gene family in Z. armatum and emphasizes the crucial role of ZaSPL21 in improving tolerance to salt and promoting flowering. The results offer potential strategies for the further utilization of these genes to improve the salt tolerance of Z. armatum.

Rosa roxburghii Tratt. is an important commercial horticultural crop endemic to China, which is recognized for its extremely high content of L-ascorbic acid (AsA). To understand the mechanisms underlying AsA overproduction in fruit of R. roxburghii, content levels, accumulation rate, and the expression of genes putatively in the biosynthesis of AsA during fruit development have been characterized. The content of AsA increased with fruit weight during development, and AsA accumulation rate was found to be highest between 60 and 90 days after anthesis (DAA), with approximately 60% of the total amount being accumulated during this period. In vitro incubating analysis of 70DAA fruit flesh tissues confirmed that AsA was synthesized mainly via the L-galactose pathway although L-Gulono-1, 4-lactone was also an effective precursor elevating AsA biosynthesis. Furthermore, in transcript level, AsA content was significantly associated with GDP-L-galactose phosphorylase (RrGGP2) gene expression. Virus-induced RrGGP2 silencing reduced the AsA content in R. roxburghii fruit by 28.9%. Overexpressing RrGGP2 increased AsA content by 8-12-fold in tobacco leaves and 2.33-3.11-fold in tomato fruit, respectively, and it showed enhanced resistance to oxidative stress caused by paraquat in transformed tobacco. These results further justified the importance of RrGGP2 as a major control step to AsA biosynthesis in R. roxburghii fruit.

Rosa roxburghii Tratt. is an emerging fruit endemic to China, which has the reputation of being the “King of Vitamin C” because of its abundance of vitamin C. However, it is also a recalcitrant species that imposes severe limitations on the transformation and whole-plant regeneration processes, restricting the verification of the functional genes. Therefore, developing a feasible and efficient genetic transformation method for R. roxburghii is an urgent requirement. Herein, K599 with eGFP was used as the Agrobacterium strain to optimize the genetic transformation from four factors: bacterial concentration, seedling age, infection site, and method. First, the original roots of 5-day-old seedlings were excised, and then the slant cuts of the remaining hypocotyls with 0.5 cm length were placed in K599 at an OD600 of 0.4. Subsequently, the explants were planted in a moistened sterile vermiculite after the beveled site was stained with a clump of bacteria. The results showed that the transformation efficiency of this cutting method was almost 28% at 30 days post-inoculation, while the transformation efficiency obtained by injecting 5-day-old seedlings 0.5–1.0 cm away from the primary root with K599 at an OD600 of 0.4 was only about 7%. Taken together, the current findings provide evidence that Agrobacterium-mediated transformation is a simple, fast, and efficient approach for generating composite R. roxburghii plants. Thus, this method has a broad application to analyze the gene functions in R. roxburghii and other related plant species.

Powdery mildew caused by Sphaerotheca sp. is the most serious disease of Rosa roxburghii cultivation. In this study, the foliar application of chitosan induced Rosa roxburghii Tratt. against Sphaerotheca sp. and its effects on the disease resistance, growth, yield, and quality of R. roxburghii were investigated. The results show that the foliar application of 1.0%~1.5% chitosan could effectively control Sphaerotheca sp. of R. roxburghii with the inducing control efficacy of 69.30%~72.87%. The foliar application of 1.0%~1.5% chitosan significantly (p < 0.01) increased proline, soluble sugar, flavonoids, superoxide dismutase (SOD), and polyphenoloxidase (POD) activities of the R. roxburghii leaf and decreased its malonaldehyde (MDA), as well as reliably enhanced its photosynthetic rate and chlorophyll. Moreover, the foliar application of 1.0%~1.5% chitosan notably improved single fruit weight, yield, vitamin C, soluble solid, soluble sugar, total acidity, soluble protein, flavonoids, and SOD activity of R. roxburghii fruits. This study highlights that chitosan can be used as an ideal, efficient, safe, and economical inductor for controlling powdery mildew of R. Roxburgh and enhancing its resistance, growth, yield, and quality.

Chestnut rose, R. roxburghii Tratt. (Rosaceae) (RR) is an important crop in China due to its nutritional and medicinal values. RR frequently produces trichomes on the surfaces of a diverse range of organs, however a genetic component exists to the control of trichome development, with some cultivars having significantly fewer trichomes to others. Certain varieties have fruits that are thickly covered with macroscopic trichomes, which is an undesirable trait for fruit processing and consumption. However, smooth‐fruit cultivars exist, such as R. roxburghii Tratt. f. esetosa Ku (RRE). Despite their economic importance, the anatomical features of trichomes have not been explored in detail for these two chestnut rose germplasms. Here, we investigate the ultrastructure of trichomes distributed on the stem, sepal, and fruit of RR and RRE using transmission electron microscopy (TEM). The internal structure of stem prickle trichomes in RR and RRE was oval in shape and did not contain nucleoli or other organelles. The cell walls of stem prickles in RR are thick and the intercellular spaces occupied with liquid, whereas the cells wall of stem prickles in RRE are thin and have air‐filled intercellular spaces. The cells of sepal acicular trichomes in RR and glandular trichomes (GTs) of sepals in RRE had similar vacuole sizes, cytoplasm content, intercellular spaces, and arrangement of plastids within cells. However, there were osmiophilic granules present in the GTs of RRE. The flagelliform trichomes in the sepals of the two germplasms are composed of oval or rod‐shaped cells. Although the flagelliform trichomes in the sepals of the two germplasms had a similar internal structure, and both contained starch grains and plastids with visible thylakoid membranes, the flagelliform trichomes in the sepals of RR had a thinner cell wall and a higher proportion of cytoplasm which was more evenly distributed across the cell. There were granules that stained heavily with osmium tetroxide which occurred infrequently in the flagelliform trichomes of sepals in RRE but were not observed in RR. On the acicular trichomes of fruit in RR, the flagelliform trichomes and the GTs of fruit in RRE shared similar cell morphology, arrangement and vacuole size as well as intercellular space. Both the fruit flagelliform trichomes and GTs in RRE contain granules which stain heavily with osmium tetroxide, and the GTs contain plastids and starch grains. These differences in trichome cell ultrastructure may be related to developmental processes or biological functions of the trichomes. These results also suggest that the two chestnut rose germplasms are good candidates for further study of trichome ontogeny in the genus and subsequent breeding of the smooth organ trait in this species.

Dof (DNA binding with one finger) proteins play important roles in plant development and defense regulatory networks. In the present study, we report a genome-wide analysis of rose Dof genes (RchDof), including phylogenetic inferences, gene structures, chromosomal locations, gene duplications, and expression diversity. A total of 24 full-length RchDof genes were identified in Rosa chinensis, which were assigned to nine distinct subgroups. These RchDof genes were unevenly distributed on rose chromosomes. The genome-scale analysis of synteny indicated that segmental duplication events may have played a major role in the evolution of the RchDof gene family. Analysis of cis-acting elements revealed putative functions of Dofs in rose during development as well as under numerous biotic and abiotic stress conditions. Moreover, the expression profiles derived from qRT-PCR experiments demonstrated distinct expression patterns in various tissues, and gene expression divergence existed among the duplicated RchDof genes, suggesting a fundamentally functional divergence of the duplicated Dof paralogs in rose. The gene expression analysis of RchDofs under drought and salt stress conditions was also performed. The present study offered novel insights into the evolution of RchDofs and can aid in the further functional characterization of its candidate genes.