Search

S -adenosyl- l -methionine (SAM) is the methyl donor involved in the biosynthesis of guaiacyl (G) and syringyl (S) lignins in vascular plants. SAM is synthesized from methionine through the catalysis of the enzyme S -adenosylmethionine synthase (SAMS). However, the detailed function of SAMS in lignin biosynthesis has not been widely investigated in plants, particularly in monocot species. In this study, we identified PvSAMS genes from switchgrass (Panicum virgatum L.), an important dual-purpose fodder and biofuel crop, and generated numerous transgenic switchgrass lines through PvSAMS RNA interference technology. Down-regulation of PvSAMS reduced the contents of SAM, G-lignins, and S-lignins in the transgenic switchgrass. The methionine and glucoside derivatives of caffeoyl alcohol were found to accumulate in the transgenic plants. Moreover, down-regulation of PvSAMS in switchgrass resulted in brownish stems associated with reduced lignin content and improved cell wall digestibility. Furthermore, transcriptomic analysis revealed that most sulfur deficiency-responsive genes were differentially expressed in the transgenic switchgrass, leading to a significant increase in total sulfur content; thus implying an important role of SAMS in the methionine cycle, lignin biosynthesis, and sulfur assimilation. Taken together, our results suggest that SAMS is a valuable target in lignin manipulation, and that manipulation of PvSAMS can simultaneously regulate the biosynthesis of SAM and methylated monolignols in switchgrass. [ABSTRACT FROM AUTHOR]

Switchgrass (Panicum virgatum L.) is an important perennial, noninvasive, tall ornamental grass that adds color and texture to gardens and landscapes. Moreover, switchgrass has been considered a forage and bioenergy crop because of its vigorous growth, low-input requirements, and broad geography. Here, we identified PvWOX3a from switchgrass, which encodes a WUSCHEL-related homeobox transcription factor. Transgenic overexpression of PvWOX3a in switchgrass increased stem length, internode diameter, and leaf blade length and width, all of which contributed to a 95% average increase in dry weight biomass compared with control plants. Yeast one-hybrid and transient dual-luciferase assays showed that PvWOX3a can repress the expression of gibberellin 2-oxidase and cytokinin oxidase/dehydrogenase through apparently direct interaction with their promoter sequences. These results suggested that overexpression of PvWOX3a could increase gibberellin and cytokinin levels in transgenic switchgrass plants, which promotes cell division, elongation, and vascular bundle development. We also overexpressed PvWOX3a in a transgenic miR156-overexpressing switchgrass line that characteristically exhibited more tillers, thinner internodes, and narrower leaf blades. Double transgenic switchgrass plants displayed significant increases in internode length and diameter, leaf blade width, and plant height but retained a tiller number comparable to that of plants expressing miR156 alone. Ultimately, the double transgenic switchgrass plants produced 174% more dry-weight biomass and 162% more solubilized sugars on average than control plants. These findings indicated that PvWOX3a is a viable potential genetic target for engineering improved shoot architecture and biomass yield of horticulture, fodder, and biofuel crops. [ABSTRACT FROM AUTHOR]

Medicago polymorpha is a nutritious and palatable forage and vegetable plant that also fixes nitrogen. Here, we reveal the chromosome-scale genome sequence of M. polymorpha using an integrated approach including Illumina, PacBio and Hi-C technologies. We combined PacBio full-length RNA-seq, metabolomic analysis, structural anatomy analysis and related physiological indexes to elucidate the important agronomic traits of M. polymorpha for forage and vegetable usage. The assembled M. polymorpha genome consisted of 457.53 Mb with a long scaffold N50 of 57.72 Mb, and 92.92% (441.83 Mb) of the assembly was assigned to seven pseudochromosomes. Comparative genomic analysis revealed that expansion and contraction of the photosynthesis and lignin biosynthetic gene families, respectively, led to enhancement of nutritious compounds and reduced lignin biosynthesis in M. polymorpha. In addition, we found that several positively selected nitrogen metabolism-related genes were responsible for crude protein biosynthesis. Notably, the metabolomic results revealed that a large number of flavonoids, vitamins, alkaloids, and terpenoids were enriched in M. polymorpha. These results imply that the decreased lignin content but relatively high nutrient content of M. polymorpha enhance its edibility and nutritional value as a forage and vegetable. Our genomic data provide a genetic basis that will accelerate functional genomic and breeding research on M. polymorpha as well as other Medicago and legume plants. [ABSTRACT FROM AUTHOR]

Anthocyanins biosynthesized from the flavonoid pathway are types of pigments that are involved in the protection of poplar from biotic and abiotic stresses. Previous researchers studying anthocyanin-related transcription factors and structural genes in poplar have made significant discoveries. However, little is known about the regulatory role of microRNAs in anthocyanin biosynthesis in poplar. Here, we overexpressed miR156 in poplar to study the comprehensive effects of the miR156-SPL module on the biosynthesis of anthocyanins. Small RNA sequencing analysis revealed 228 microRNAs differentially expressed in transgenic poplar plants with dramatically increased miR156 levels. Furthermore, integrated microRNAomic and transcriptomic analysis suggested that two microRNAs, miR160h, and miR858, have the potential to affect anthocyanin accumulation in poplar by regulating auxin response factors and MYB transcription factors, respectively. Additionally, the accumulation of miR160h and miR858 displayed a positive correlation with miR156 levels, suggesting a possible interaction between the miR156-SPL module and these microRNAs in poplar. Last, metabolomics analysis revealed that the levels of anthocyanins, flavones, and flavonols were substantially elevated in transgenic poplar plants overexpressing miR156 compared with the wild type, whereas the total lignin content was reduced in the transgenic plants. Taken together, our results indicate that miR156 can fine tune the anthocyanin biosynthetic pathway via multiple factors, including microRNAs, transcription factors, and the levels of structural genes, in poplar. This provides additional clues for understanding the complex regulatory network of anthocyanin biosynthesis in woody plants. [ABSTRACT FROM AUTHOR]

The brown midrib2 (bm2) mutant of maize, which has a modified lignin composition, contains a mutation in the methylenetetrahydrofolate reductase (MTHFR) gene. Here, we show that a MITE transposon insertion caused down-regulation of MTHFR , with an accompanying decrease in 5-methyl-tetrahydrofolate and an increase in 5, 10-methylene-tetrahydrofolate and tetrahydrofolate in the bm2 mutant. Furthermore, MTHFR mutation did not change the content of S -adenosyl methionine (SAM), the methyl group donor involved in the biosynthesis of guaiacyl and syringyl lignins, but increased the level of S -adenosyl homocysteine (SAH), the demethylation product of SAM. Moreover, competitive inhibition of the maize caffeoyl CoA O -methyltransferase (CCoAOMT) and caffeic acid O -methyltransferase (COMT) enzyme activities by SAH was found, suggesting that the SAH/SAM ratio, rather than the concentration of SAM, regulates the transmethylation reactions of lignin intermediates. Phenolic profiling revealed that caffeoyl alcohol glucose derivatives accumulated in the bm2 mutant, indicating impaired 3- O -methylation of monolignols. A remarkable increase in the unusual catechyl lignin in the mutant demonstrates that MTHFR down-regulation mainly affects guaiacyl lignin biosynthesis, consistent with the observation that CCoAOMT is more sensitive to SAH inhibition than COMT. This study uncovered a novel regulatory mechanism in lignin biosynthesis, which may offer an effective approach to utilizing lignocellulosic feedstocks in the future. [ABSTRACT FROM AUTHOR]