Analyzing lignin biosynthesis pathways in rattan using improved co-expression networks of NACs and MYBs

Identification of key genes involved in lignin and flavonoid accumulation during Tilia tuan seed maturation

KEY MESSAGE

Transcriptomics and phenotypic data analysis identified 24 transcription factors (TFs) that play key roles in regulating the competitive accumulation of lignin and flavonoids. Tilia tuan Szyszyl. (T. tuan) is a timber tree species with important ecological and commercial value. However, its highly lignified pericarp results in a low seed germination rate and a long dormancy period. In addition, it is unknown whether there is an interaction between the biosynthesis of flavonoids and lignin as products of the phenylpropanoid pathway during seed development. To explore the molecular regulatory mechanism of lignin and flavonoid biosynthesis, T. tuan seeds were harvested at five stages (30, 60, 90, 120, and 150 days after pollination) for lignin and flavonoid analyses. The results showed that lignin accumulated rapidly in the early and middle stages (S1, S3, and S4), and rapid accumulation of flavonoids during the early and late stages (S1 and S5). High-throughput RNA sequencing analysis of developing seeds identified 50,553 transcripts, including 223 phenylpropanoid biosynthetic pathway genes involved in lignin accumulation grouped into 3 clusters, and 106 flavonoid biosynthetic pathway genes (FBPGs) grouped into 2 clusters. Subsequent WGCNA and time-ordered gene co-expression network (TO-GCN) analysis revealed that 24 TFs (e.g., TtARF2 and TtWRKY15) were involved in flavonoids and lignin biosynthesis regulation. The transcriptome data were validated by qRT-PCR to analyze the expression profiles of key enzyme-coding genes. This study revealed that there existed a competitive relationship between flavonoid and lignin biosynthesis pathway during the development of T. tuan seeds, that provide a foundation for the further exploration of molecular mechanisms underlying lignin and flavonoid accumulation in T. tuan seeds.

Adaptation mechanism of three Impatiens species to different habitats based on stem morphology, lignin and MYB4 gene

BACKGROUND

Impatiens is an important genus with rich species of garden plants, and its distribution is extremely extensive, which is reflected in its diverse ecological environment. However, the specific mechanisms of Impatiens' adaptation to various environments and the mechanism related to lignin remain unclear.

RESULTS

Three representative Impatiens species,Impatiens chlorosepala (wet, low degree of lignification), Impatiens uliginosa (aquatic, moderate degree of lignification) and Impatiens rubrostriata (terrestrial, high degree of lignification), were selected and analyzed for their anatomical structures, lignin content and composition, and lignin-related gene expression. There are significant differences in anatomical parameters among the stems of three Impatiens species, and the anatomical structure is consistent with the determination results of lignin content. Furthermore, the thickness of the xylem and cell walls, as well as the ratio of cell wall thickness to stem diameter have a strong correlation with lignin content. The anatomical structure and degree of lignification in Impatiens can be attributed to the plant's growth environment, morphology, and growth rate. Our analysis of lignin-related genes revealed a negative correlation between the MYB4 gene and lignin content. The MYB4 gene may control the lignin synthesis in Impatiens by controlling the structural genes involved in the lignin synthesis pathway, such as HCT, C3H, and COMT. Nonetheless, the regulation pathway differs between species of Impatiens.

CONCLUSIONS

This study demonstrated consistency between the stem anatomy of Impatiens and the results obtained from lignin content and composition analyses. It is speculated that MYB4 negatively regulates the lignin synthesis in the stems of three Impatiens species by regulating the expression of structural genes, and its regulation mechanism appears to vary across different Impatiens species. This study analyses the variations among different Impatiens plants in diverse habitats, and can guide further molecular investigations of lignin biosynthesis in Impatiens.

Large-scale analysis of putative Euphorbiaceae R2R3-MYB transcription factors identifies a MYB involved in seed oil biosynthesis

BACKGROUND

MYB transcription factors are widely distributed in the plant kingdom and play key roles in regulatory networks governing plant metabolism and biochemical and physiological processes.

RESULTS

Here, we first determined the R2R3-MYB genes in five Euphorbiaceae genomes. The three Trp (W) residues from the first MYB domain (R2) were absolutely conserved, whereas the first W residue from the second MYB domain (R3) was preferentially mutated. The R2R3-MYBs were clustered into 48 functional subfamilies, of which 34 had both R2R3-MYBs of Euphorbiaceae species and AtMYBs, and four contained only Euphorbiaceae R2R3-MYBs. The whole-genome duplication (WGD) and/or segmental duplication (SD) played key roles in the expansion of the R2R3-MYB family. Unlike paralogous R2R3-MYB family members, orthologous R2R3-MYB members contained a higher selective pressure and were subject to a constrained evolutionary rate. VfMYB36 was specifically expressed in fruit, and its trend was consistent with the change in oil content, indicating that it might be involved in oil biosynthesis. Overexpression experiments showed that VfMYB36 could significantly provide linolenic acid (C18:3) content, which eventually led to a significant increase in oil content.

CONCLUSION

Our study first provides insight into understanding the evolution and expression of R2R3-MYBs in Euphorbiaceae species, and also provides a target for the production of biomass diesel and a convenient way for breeding germplasm resources with high linolenic acid content in the future.

Integrated metabolome, transcriptome analysis, and multi-flux full-length sequencing offer novel insights into the function of lignin biosynthesis as a Sesuvium portulacastrum response to salt stress

Sesuvium portulacastrum is a typical halophyte. However, few studies have investigated its salt-tolerant molecular mechanism. In this study, metabolome, transcriptome, and multi-flux full-length sequencing analysis were conducted to investigate the significantly different metabolites (SDMs) and differentially expressed genes (DEGs) of S. portulacastrum samples under salinity. The complete-length transcriptome of S. portulacastrum was developed, which contained 39,659 non-redundant unigenes. RNA-seq results showed that 52 DEGs involved in lignin biosynthesis may be responsible for S. portulacastrum salt tolerance. Furthermore, 130 SDMs were identified, and the salt response could be attributed to the p-coumaryl alcohol-rich in lignin biosynthesis. The co-expression network that was constructed after comparing the different salt treatment processes showed that the p-Coumaryl alcohol was linked to 30 DEGs. Herein, 8 structures genes, i.e., Sp4CL, SpCAD, SpCCR, SpCOMT, SpF5H, SpCYP73A, SpCCoAOMT, and SpC3'H were identified as significant factors in regulating lignin biosynthesis. Further investigation revealed that 64 putative transcription factors (TFs) may interact with the promoters of the above-mentioned genes. Together, the data revealed a potential regulatory network comprising important genes, putative TFs, and metabolites involved in the lignin biosynthesis of S. portulacastrum roots under salt stress, which could serve as a rich useful genetic resource for breeding excellent salt-tolerant plants.