Lignin is a phenylpropanoid-derived polymer that functions as a major component of cell walls in plant vascular tissues. Biosynthesis of the aromatic amino acid Phe provides precursors for many ...secondary metabolites, including lignins and flavonoids. Here, we discovered that MYB transcription factors MYB20, MYB42, MYB43, and MYB85 are transcriptional regulators that directly activate lignin biosynthesis genes and Phe biosynthesis genes during secondary wall formation in Arabidopsis (
). Disruption of
,
,
, and
resulted in growth development defects and substantial reductions in lignin biosynthesis. In addition, our data showed that these MYB proteins directly activated transcriptional repressors that specifically inhibit flavonoid biosynthesis, which competes with lignin biosynthesis for Phe precursors. Together, our results provide important insights into the molecular framework for the lignin biosynthesis pathway.
Lodging under nitrogen (N)-luxury conditions substantially reduces crop yield and seed quality. However, the molecular mechanisms of plant lodging resistance remain largely unclear, especially in ...maize. We report here that the expression of ZmmiR528, a monocot-specific microRNA, is induced by N luxury but reduced by N deficiency. We show by the thioacidolysis and acetyl bromide analysis that N luxury significantly reduces the generation of H, G, and S monomers of the lignin as well as its total content in maize shoots. We further demonstrate that ZmLACCASE3 (ZmLAC3) and ZmLACCASE5 (ZmLAC5), which encode the copper-containing laccases, are the targets of ZmmiR528. In situ hybridization showed that ZmmiR528 is mainly expressed in maize vascular tissues. Knockdown of ZmmiR528 or overexpression of ZmLAC3 significantly increased the lignin content and rind penetrometer resistance of maize stems. In contrast, transgenic maize plants overexpressing ZmmiR528 had reduced lignin content and rind penetrometer resistance and were prone to lodging under N-luxury conditions. RNA-sequencing analysis revealed that ZmPAL7 and ZmPAL8 are upregulated in transgenic maize lines downregulating ZmmiR528. Under N-luxury conditions, the expression levels of ZmPALs were much higher in ZmmiR528-knockdown lines than in the wild type and transgenic maize lines overexpressing ZmmiR528. Taken together, these results indicate that, by regulating the expression of ZmLAC3 and ZmLAC5, ZmmiR528 affects maize lodging resistance under N-luxury conditions.
This study quantitatively determined that the maize lodging under N-luxury conditions results in part from a reduction in the contents of lignin monomers and total lignin. Unlike miR528 in rice, which functions in immune responses, ZmmiR528 affects lignin biosynthesis in maize by negative regulation of ZmLACs. Zm-miRNA528 and ZmLAC modules might be useful for improving the agronomic traits of maize.
Abstract
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
Changes in atmospheric CO
2
concentration have played a central role in algal and plant adaptation and evolution. The commercially important red algal genus,
Pyropia
(Bangiales) appears to ...have responded to inorganic carbon (C
i
) availability by evolving alternating heteromorphic generations that occupy distinct habitats. The leafy gametophyte inhabits the intertidal zone that undergoes frequent emersion, whereas the sporophyte conchocelis bores into mollusk shells. Here, we analyze a high-quality genome assembly of
Pyropia yezoensis
to elucidate the interplay between C
i
availability and life cycle evolution. We find horizontal gene transfers from bacteria and expansion of gene families (e.g. carbonic anhydrase, anti-oxidative related genes), many of which show gametophyte-specific expression or significant up-regulation in gametophyte in response to dehydration. In conchocelis, the release of HCO
3
-
from shell promoted by carbonic anhydrase provides a source of C
i
. This hypothesis is supported by the incorporation of
13
C isotope by conchocelis when co-cultured with
13
C-labeled CaCO
3
.
Summary
Switchgrass (Panicum virgatum L.) has been developed into a dedicated herbaceous bioenergy crop. Biomass yield is a major target trait for genetic improvement of switchgrass. microRNAs have ...emerged as a prominent class of gene regulatory factors that has the potential to improve complex traits such as biomass yield. A miR156b precursor was overexpressed in switchgrass. The effects of miR156 overexpression on SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) genes were revealed by microarray and quantitative RT‐PCR analyses. Morphological alterations, biomass yield, saccharification efficiency and forage digestibility of the transgenic plants were characterized. miR156 controls apical dominance and floral transition in switchgrass by suppressing its target SPL genes. Relatively low levels of miR156 overexpression were sufficient to increase biomass yield while producing plants with normal flowering time. Moderate levels of miR156 led to improved biomass but the plants were non‐flowering. These two groups of plants produced 58%–101% more biomass yield compared with the control. However, high miR156 levels resulted in severely stunted growth. The degree of morphological alterations of the transgenic switchgrass depends on miR156 level. Compared with floral transition, a lower miR156 level is required to disrupt apical dominance. The improvement in biomass yield was mainly because of the increase in tiller number. Targeted overexpression of miR156 also improved solubilized sugar yield and forage digestibility, and offered an effective approach for transgene containment.
The root stem cell niche, which is composed of four mitotically inactive quiescent center (QC) cells and the surrounding actively divided stem cells in Arabidopsis, is critical for growth and root ...development. Here, we demonstrate that the Arabidopsis prohibitin protein PHB3 is required for the maintenance of root stem cell niche identity by both inhibiting proliferative processes in the QC and stimulating cell division in the proximal meristem (PM). PHB3 coordinates cell division and differentiation in the root apical meristem by restricting the spatial expression of ethylene response factor (ERF) transcription factors 115, 114, and 109. ERF115, ERF114, and ERF109 mediate ROS signaling, in a PLT-independent manner, to control root stem cell niche maintenance and root growth through phytosulfokine (PSK) peptide hormones in Arabidopsis.
Display omitted
•Prohibitin proteins act as common stem cell regulators in mammals and plants•ERF115, ERF114, and ERF109 are ROS-responsive factors that maintain root SCN identity•PHB3 restricts the spatial expression patterns of ERF115, ERF114, and ERF109 in roots
Prohibitins (PHBs) have been identified as negative regulators of the cell cycle. Here, Kong et al. demonstrate that Arabidopsis PHB3 is essential to maintain QC and DSC identity, and it controls root meristem activity by restricting the spatial expression of the ROS-responsive factors ERF115, 114, and 109 in root.
Switchgrass is a leading dedicated bioenergy feedstock in the United States because it is a native, high-yielding, perennial prairie grass with a broad cultivation range and low agronomic input ...requirements. Biomass conversion research has developed processes for production of ethanol and other biofuels, but they remain costly primarily because of the intrinsic recalcitrance of biomass. We show here that genetic modification of switchgrass can produce phenotypically normal plants that have reduced thermal-chemical (less-than or equal to180 °C), enzymatic, and microbial recalcitrance. Down-regulation of the switchgrass caffeic acid O-methyltransferase gene decreases lignin content modestly, reduces the syringyl:guaiacyl lignin monomer ratio, improves forage quality, and, most importantly, increases the ethanol yield by up to 38% using conventional biomass fermentation processes. The down-regulated lines require less severe pretreatment and 300-400% lower cellulase dosages for equivalent product yields using simultaneous saccharification and fermentation with yeast. Furthermore, fermentation of diluted acid-pretreated transgenic switchgrass using Clostridium thermocellum with no added enzymes showed better product yields than obtained with unmodified switchgrass. Therefore, this apparent reduction in the recalcitrance of transgenic switchgrass has the potential to lower processing costs for biomass fermentation-derived fuels and chemicals significantly. Alternatively, such modified transgenic switchgrass lines should yield significantly more fermentation chemicals per hectare under identical process conditions.
High levels of salinity induce serious oxidative damage in plants. Flavonoids, as antioxidants, have important roles in reactive oxygen species (ROS) scavenging. In the present study, the tobacco ...R2R3 MYB type repressor, NtMYB4, was isolated and characterized. The expression of
was suppressed by salinity. Overexpression of
reduced the salt tolerance in transgenic tobacco plants. NtMYB4 repressed the promoter activity of
and negatively regulated its expression. Rutin accumulation was significantly decreased in
overexpressing transgenic plants and
RNAi silenced transgenic plants. Moreover, high H
O
and
contents were detected in both types of rutin-reduced transgenic plants under high salt stress. In addition, exogenous rutin supplementation effectively scavenged ROS (H
O
and
) and improved the salt tolerance of the rutin-reduced transgenic plants. In contrast,
overexpressing plants had increased rutin accumulation, lower H
O
and
contents, and higher tolerance to salinity. These results suggested that tobacco NtMYB4 acts as a salinity response repressor and negatively regulates
expression, which results in the reduced flavonoid accumulation and weakened ROS-scavenging ability under salt stress.
The ability to create targeted mutations using clustered regularly inter-spaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) 9 in support of forest tree biotechnology is currently ...limited. CRISPR/Cas12a is a novel CRISPR effector protein that not only broadens the CRISPR/Cas targeting range but also enables the generation of large-fragment deletions. In this study, a CRISPR/Cas12a system was evaluated for the induction of targeted mutations in the woody tree poplar (
×
). Three Cas12a nucleases, namely, AsCas12a (
sp. BV3L6), LbCas12a (Lachnospiraceae bacterium ND2006), and FnCas12a (
subsp.
U112), were used. We knocked out multiple targets of the
(
) using the CRISPR/Cas12a genome-targeting system, and the results indicated that the AsCas12a system is the most efficient. We further optimized the co-cultivation temperature after
-mediated transformation from 22 to 28°C to increase the Cas12a nuclease editing efficiency in poplar. AsCas12a showed the highest mutation efficiency, at 70%, and the majority of editing sites were composed of large-fragment deletions. By using this simple and high-efficiency CRISPR/Cas12a system, multiple targets can be modified to obtain multigene simultaneous knockout mutants in tree species, which will provide powerful tools with which to facilitate genetic studies of forest trees.
Summary
Ferulate 5‐hydroxylase (F5H) catalyses the hydroxylation of coniferyl alcohol and coniferaldehyde for the biosynthesis of syringyl (S) lignin in angiosperms. However, the coordinated effects ...of F5H with caffeic acid O‐methyltransferase (COMT) on the metabolic flux towards S units are largely unknown. We concomitantly regulated F5H expression in COMT‐down‐regulated transgenic switchgrass (Panicum virgatum L.) lines and studied the coordination of F5H and COMT in lignin biosynthesis. Down‐regulation of F5H in COMT‐RNAi transgenic switchgrass plants further impeded S lignin biosynthesis and, consequently, increased guaiacyl (G) units and reduced 5‐OH G units. Conversely, overexpression of F5H in COMT‐RNAi transgenic plants reduced G units and increased 5‐OH units, whereas the deficiency of S lignin biosynthesis was partially compensated or fully restored, depending on the extent of COMT down‐regulation in switchgrass. Moreover, simultaneous regulation of F5H and COMT expression had different effects on cell wall digestibility of switchgrass without biomass loss. Our results indicate that up‐regulation and down‐regulation of F5H expression, respectively, have antagonistic and synergistic effects on the reduction in S lignin resulting from COMT suppression. The coordinated effects between lignin genes should be taken into account in future studies aimed at cell wall bioengineering.
PDF
