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The genus Apocynum contains perennial bast fiber plants that are spread worldwide. Apocynum species have great application prospect in salt-alkali regions, are rich in flavonoids, and possess medicinal significance. Here, we report the draft genomes of two species, Apocynum venetum and Apocynum hendersonii, and elucidate their evolutionary relationship. The high synteny and collinearity between A. venetum and A. hendersonii suggested that the two species experienced the same WDG event, indicating that divergence might be more recent. Comparative analysis revealed that ApF3H and differentially evolved ApUFGT genes are critical for determining natural variation in flavonoid biosynthesis between relatives. ApF3H-1 enhanced the total flavonoid content and promoted the antioxidant capacity of transformed plants compared to the wild-type plant. ApUFGT5 and 6 explained the diversification of flavonoids or their derivatives. These data provide biochemical insight and knowledge on the genetic regulation of flavonoid biosynthesis, supporting the adoption of these genes in breeding programs aimed at the multipurpose use of plants.

AP2/ERF transcription factors (TFs) are one of the largest superfamilies in plants, and play vital roles in growth and response to biotic/abiotic stresses. Although the AP2/ERF family has been extensively characterized in many species, very little is known about this family in ramie (

A total of 60 WRKY family genes of ramie were identified in the ramie. The genes were unevenly distributed across 14 chromosomes in the specie and highly concentrated (72%) in the distal telomeric region. Phylogenetic analysis placed these genes into seven distinct subfamilies groups: I, II (a, b, c, d, e), and III, with group IIc containing only the variant of heptapetide sequence (WRKYGKK). Segmental duplication events (41.7%) was found to be the main driver of BnGWRKY evolution. Thirty eight from among the genes showed collinear relationships with WRKY genes from

MYB transcription factors are crucial in regulating stress tolerance and expression of major genes involved in flavonoid biosynthesis. The functions of MYBs is well explored in a number of plants, yet no study is reported in Apocynum venetum. We identified a total of 163 MYB candidates, that comprised of 101 (61.96%) R2R3, 6 3R, 1 4R and 55 1R. Syntenic analysis of A. venetum R2R3 (AvMYBs) showed highest orthologous pairs with Vitis vinifera MYBs followed by Arabidopsis thaliana among the four species evaluated. Thirty segmental duplications and 6 tandem duplications were obtained among AvMYB gene pairs signifying their role in the MYB gene family expansion. Nucleotide substitution analysis (Ka/Ks) showed the AvMYBs to be under the influence of strong purifying selection. Expression analysis of selected AvMYBs under low temperature and cadmium stresses resulted in the identification of AvMYB48, AvMYB97, AvMYB8, AvMYB4 as potential stress responsive genes and AvMYB10 and AvMYB11 in addition, proanthocyanidin biosynthesis regulatory genes which is consistent with their annotated homologues in Arabidopsis. Tissue specific expression profile analysis of the AvMYBs further supported the qPCR analysis result. MYBs with higher transcript levels in root, stem and leaf like AvMYB4 for example, was downregulated under the stresses and such with low transcript level such as AvMYB48 which had low transcript in the leaf was upregulated under both stresses. Transcriptome and phylogenetic analyses suggested AvMYB42 as a potential regulator of anthocyanin biosynthesis. Thus, this study provided valuable information on AvR2R3-MYB gene family with respect to stress tolerance and flavonoid biosynthesis.

Lint percentage is an important cotton (Gossipium hirsutum L.) lint yield character which may have a close association with photoassimilates partitioning between fibers and seeds. A three-year field experiment was conducted with an aim to determine whether or not the formation of lint percentage is associated with sucrose metabolism in both of fibers and seeds, and potential contributors to the performance of lint percentage. Two upland cotton (Gossypium hirsutum L.) lines A705 and A201 differing in lint percentage and seed size were employed to examine genotypic difference in within-boll yield components, nonstructural carbohydrate components (hexose, sucrose and starch) and key sucrose metabolism enzymes across 2015–2017. A705 had greater lint mass per boll, lint index, and higher lint percentage and cellulose content in fibers, but smaller boll weight, seed mass per boll, seed index and lower oil content in embryos compared to A201. The result indicated that the fiber sink strength was greater in A705 than in A201, but the reverse was true of the seed sink strength. A705 exhibited consistently higher sucrose concentration and sucrose synthase (Sus) activity in fibers during fiber development relative to A201, while the latter recorded consistently higher sucrose concentration and Sus activity in younger ovules during 5–17 days post anthesis (DPA) and in older embryos and seed coats during 24 DPA to 45 DPA. Higher starch concentration and sucrose phosphate synthase (SPS) activity with seed coats were detected in A705 than in A201, implying sucrose synthesized by SPS in A705 at sink storage stage is preferentially partitioned to starch biosynthesis in seed coats. It is concluded that a higher lint percentage in A705 than in A201 is attributable to a combination of greater fiber sink strength and smaller seed sink strength available in the former relative to the latter. Sucrose and Sus may function as key biomarkers for assessing fiber and ovule sink strengths.

A field study was conducted in 2013 and 2014 where cotton was exposed to three N regimes: (1) the control without N application (low N); (2) 260 kg N ha−1 (medium N); (3) 520 kg N ha−1 (high N). Boll size, lint mass per boll, seed mass per boll, fiber length and strength were significantly decreased under N deprivation in the two years. The increased carbohydrate levels of LSCB (leaf subtending the cotton boll) led to decreased carbohydrate levels of fibers in the low N relative to the other N treatments. The low N embryos exhibited lower starch concentrations at 17 and 31 DPA (days post anthesis), and TNC (total nonstructural carbohydrate) concentrations at 17, 31, 45 and 52 DPA compared to medium N embryos. Starch levels in LSCB had negative associations with those in fibers at 17, 31 and 45 DPA, but positive associations with those in embryos at 24 and 45 DPA. Fibers expressed negative associations with embryos in glucose level at 24 and 38 DPA, and in TNC levels at 17 and 45 DPA. The study sug...

The accumulation level of soluble carbohydrates in fibers during flowering may affect the final fiber length in upland cotton (Gossypium hirsutum L.). The objective of this study was to determine the relationship of carbohydrate levels and carbon metabolism enzyme activities in fibers to fiber elongation under water deficit stress. A pot study was conducted in 2013 with treatments consisting of control (well-watered) and water stress using two cotton genotypes differing in drought tolerance, namely S011 (drought sensitive) and T886 (drought tolerant). Water stress treatment was designed as withholding water from the pots until stomatal closure followed by limited water supply for 25 days where water-stressed plants received 40% of optimum quantity of water. The results showed that the glucose, fructose, sucrose and starch concentrations decreased in water-stressed fibers compared to the control. The degree of decline in hexose and total soluble sugar concentrations under water deficit stress was higher in the sensitive genotype (S011) than the tolerant genotype (T886). Similar changes were also observed in vacuolar invertase (VIN) and sucrose synthase (SuSy) activities. The reduction in hexose concentration might be due to decreased sucrose-cleaving enzyme activities especially VIN activity. The study showed that drought stress decreased VIN and SuSy activities, and hence hexose concentration in fiber cells, which resulted in a slower fiber elongation compared to the control.