Role of xyloglucan in cotton (Gossypium hirsutum L.) fiber elongation of the short fiber mutant Ligon lintless-2 (Li2)

GhMYB30-GhMUR3 affects fiber elongation and secondary wall thickening in cotton

Xyloglucan, an important hemicellulose, plays a crucial role in maintaining cell wall structure and cell elongation. However, the effects of xyloglucan on cotton fiber development are not well understood. GhMUR3 encodes a xyloglucan galactosyltransferase that is essential for xyloglucan synthesis and is highly expressed during fiber elongation. In this study, we report that GhMUR3 participates in cotton fiber development under the regulation of GhMYB30. Overexpression GhMUR3 affects the fiber elongation and cell wall thickening. Transcriptome showed that the expression of genes involved in secondary cell wall synthesis was prematurely activated in OE-MUR3 lines. In addition, GhMYB30 was identified as a key regulator of GhMUR3 by Y1H, Dual-Luc, and electrophoretic mobility shift assay (EMSA) assays. GhMYB30 directly bound the GhMUR3 promoter and activated GhMUR3 expression. Furthermore, DAP-seq of GhMYB30 was performed to identify its target genes in the whole genome. The results showed that many target genes were associated with fiber development, including cell wall synthesis-related genes, BR-related genes, reactive oxygen species pathway genes, and VLCFA synthesis genes. It was demonstrated that GhMYB30 may regulate fiber development through multiple pathways. Additionally, GhMYB46 was confirmed to be a target gene of GhMYB30 by EMSA, and GhMYB46 was significantly increased in GhMYB30-silenced lines, indicating that GhMYB30 inhibited GhMYB46 expression. Overall, these results revealed that GhMUR3 under the regulation of GhMYB30 and plays an essential role in cotton fiber elongation and secondary wall thickening. Additionally, GhMYB30 plays an important role in the regulation of fiber development and regulates fiber secondary wall synthesis by inhibiting the expression of GhMYB46.

The final piece of the Triangle of U: Evolution of the tetraploid Brassica carinata genome

Ethiopian mustard (Brassica carinata) is an ancient crop with remarkable stress resilience and a desirable seed fatty acid profile for biofuel uses. Brassica carinata is one of six Brassica species that share three major genomes from three diploid species (AA, BB, and CC) that spontaneously hybridized in a pairwise manner to form three allotetraploid species (AABB, AACC, and BBCC). Of the genomes of these species, that of B. carinata is the least understood. Here, we report a chromosome scale 1.31-Gbp genome assembly with 156.9-fold sequencing coverage for B. carinata, completing the reference genomes comprising the classic Triangle of U, a classical theory of the evolutionary relationships among these six species. Our assembly provides insights into the hybridization event that led to the current B. carinata genome and the genomic features that gave rise to the superior agronomic traits of B. carinata. Notably, we identified an expansion of transcription factor networks and agronomically important gene families. Completion of the Triangle of U comparative genomics platform has allowed us to examine the dynamics of polyploid evolution and the role of subgenome dominance in the domestication and continuing agronomic improvement of B. carinata and other Brassica species.

Eriodictyol can modulate cellular auxin gradients to efficiently promote in vitro cotton fibre development

BACKGROUND

Flavonoids have essential roles in flower pigmentation, fibre development and disease resistance in cotton. Previous studies show that accumulation of naringenin in developing cotton fibres significantly affects fibre growth. This study focused on determining the effects of the flavonoids naringenin, dihydrokaempferol, dihydroquerectin and eriodictyol on fibre development in an in vitro system.

RESULTS

20 μM eriodictyol treatment produced a maximum fibre growth, in terms of fibre length and total fibre units. To gain insight into the associated transcriptional regulatory networks, RNA-seq analysis was performed on eriodictyol-treated elongated fibres, and computational analysis of differentially expressed genes revealed that carbohydrate metabolism and phytohormone signaling pathways were differentially modulated. Eriodictyol treatment also promoted the biosynthesis of quercetin and dihydroquerectin in ovules and elongating fibres through enhanced expression of genes encoding chalcone isomerase, chalcone synthase and flavanone 3-hydroxylase. In addition, auxin biosynthesis and signaling pathway genes were differentially expressed in eriodictyol-driven in vitro fibre elongation. In absence of auxin, eriodictyol predominantly enhanced fibre growth when the localized auxin gradient was disrupted by the auxin transport inhibitor, triiodobenzoic acid.

CONCLUSION

Eriodictyol was found to significantly enhance fibre development through accumulating and maintaining the temporal auxin gradient in developing unicellular cotton fibres.