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Sorghum mutant RG displays antithetic leaf shoot lignin accumulation resulting in improved stem saccharification properties.

Petti C, Harman-Ware AE, Tateno M, Kushwaha R, Shearer A, Downie AB, Crocker M, Debolt S - Biotechnol Biofuels (2013)

Bottom Line: Reduced lignin was linked to improved saccharification in RG stems, but a chemical shift to greater S:G ratios in RG stem lignin was also observed.Antithetic lignin accumulation was observed in the RG mutant leaf-and stem-tissue, which resulted in greater saccharification efficiency in the RG stem and differential thermochemical product yield in high lignin leaves.Thus, the red leaf coloration of the RG mutant represents a potential marker for improved conversion of stem cellulose to fermentable sugars in the C4 grass Sorghum.

View Article: PubMed Central - HTML - PubMed

Affiliation: Plant Physiology, Department of Horticulture, Agricultural Science Center North, University of Kentucky, Lexington, KY 40546, USA. sdebo2@uky.edu.

ABSTRACT

Background: Improving saccharification efficiency in bioenergy crop species remains an important challenge. Here, we report the characterization of a Sorghum (Sorghum bicolor L.) mutant, named REDforGREEN (RG), as a bioenergy feedstock.

Results: It was found that RG displayed increased accumulation of lignin in leaves and depletion in the stems, antithetic to the trend observed in wild type. Consistent with these measurements, the RG leaf tissue displayed reduced saccharification efficiency whereas the stem saccharification efficiency increased relative to wild type. Reduced lignin was linked to improved saccharification in RG stems, but a chemical shift to greater S:G ratios in RG stem lignin was also observed. Similarities in cellulose content and structure by XRD-analysis support the correlation between increased saccharification properties and reduced lignin instead of changes in the cellulose composition and/or structure.

Conclusion: Antithetic lignin accumulation was observed in the RG mutant leaf-and stem-tissue, which resulted in greater saccharification efficiency in the RG stem and differential thermochemical product yield in high lignin leaves. Thus, the red leaf coloration of the RG mutant represents a potential marker for improved conversion of stem cellulose to fermentable sugars in the C4 grass Sorghum.

No MeSH data available.


Related in: MedlinePlus

Lignin quantification from the leaf and stem of RG and wild type sorghum. (A, B, C, D) Maule’s staining for lignin in cross sections of sorghum stem (A, C) and leaf tissue (B, D). (E) Total insoluble lignin, (F) total soluble lignin; Each bar comprises the mean of four biological and four technical replicates. Error bars indicate the standard error from the mean. Significance (P < 0.05) is indicated by a star (★). Scale bar = 1 mm.
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Figure 4: Lignin quantification from the leaf and stem of RG and wild type sorghum. (A, B, C, D) Maule’s staining for lignin in cross sections of sorghum stem (A, C) and leaf tissue (B, D). (E) Total insoluble lignin, (F) total soluble lignin; Each bar comprises the mean of four biological and four technical replicates. Error bars indicate the standard error from the mean. Significance (P < 0.05) is indicated by a star (★). Scale bar = 1 mm.

Mentions: As mentioned above, the RG mutant displays visible red coloration of leaves that develops basipetally (Figure 1A). The red/purple accumulation in RG leaves was consistent with an alteration in the phenylpropanoid pathway. This pathway is also responsible for the production of lignin therefore we anticipated that the genes responsible for the production of pigments and for lignin could be altered as well. To test this hypothesis, gene expression-and chemical compositional-analyses were performed. An increase in transcript abundance was observed for key genes involved in the lignin biosynthetic branch of the phenylpropanoid pathway in RG red leaves compared with wild type (Figure 3A). The converse was true for gene expression in the stems for all but cinnamyl alcohol dehydrogenase (Figure 3B). Consistent with these data, transcript abundance extended from those genes whose products are responsible for the earliest committed metabolic conversions in the phenylpropoanoid pathway (Petti et al., cosubmitted). To establish whether lignin biosynthesis was increased, we visually observed lignin by counterstaining with phloroglucinol stain (Maule’s reagent, [29]). Here, we examined transverse cross sections of RG and wild type stems and leaves. Results illustrated a more pronounced lignin staining in the wild type stem section relative to RG (Figure 4A,C) and vice versa in the leaf (Figure 4B,D). Therefore, histochemical data suggest that stems of the RG mutant have reduced lignin biosynthesis whereas the leaves display increased levels. Transcriptional characterization of 4-week old RG and WT stems demonstrated a down-regulation for key genes involved in the lignin pathway for RG compared to the wild type, corroborating the histochemical evidence for lignin reduction (Figure 3B). One exception was CAD, whose expression was up-regulated, contradictory to reduced lignification of this tissue.


Sorghum mutant RG displays antithetic leaf shoot lignin accumulation resulting in improved stem saccharification properties.

Petti C, Harman-Ware AE, Tateno M, Kushwaha R, Shearer A, Downie AB, Crocker M, Debolt S - Biotechnol Biofuels (2013)

Lignin quantification from the leaf and stem of RG and wild type sorghum. (A, B, C, D) Maule’s staining for lignin in cross sections of sorghum stem (A, C) and leaf tissue (B, D). (E) Total insoluble lignin, (F) total soluble lignin; Each bar comprises the mean of four biological and four technical replicates. Error bars indicate the standard error from the mean. Significance (P < 0.05) is indicated by a star (★). Scale bar = 1 mm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3852544&req=5

Figure 4: Lignin quantification from the leaf and stem of RG and wild type sorghum. (A, B, C, D) Maule’s staining for lignin in cross sections of sorghum stem (A, C) and leaf tissue (B, D). (E) Total insoluble lignin, (F) total soluble lignin; Each bar comprises the mean of four biological and four technical replicates. Error bars indicate the standard error from the mean. Significance (P < 0.05) is indicated by a star (★). Scale bar = 1 mm.
Mentions: As mentioned above, the RG mutant displays visible red coloration of leaves that develops basipetally (Figure 1A). The red/purple accumulation in RG leaves was consistent with an alteration in the phenylpropanoid pathway. This pathway is also responsible for the production of lignin therefore we anticipated that the genes responsible for the production of pigments and for lignin could be altered as well. To test this hypothesis, gene expression-and chemical compositional-analyses were performed. An increase in transcript abundance was observed for key genes involved in the lignin biosynthetic branch of the phenylpropanoid pathway in RG red leaves compared with wild type (Figure 3A). The converse was true for gene expression in the stems for all but cinnamyl alcohol dehydrogenase (Figure 3B). Consistent with these data, transcript abundance extended from those genes whose products are responsible for the earliest committed metabolic conversions in the phenylpropoanoid pathway (Petti et al., cosubmitted). To establish whether lignin biosynthesis was increased, we visually observed lignin by counterstaining with phloroglucinol stain (Maule’s reagent, [29]). Here, we examined transverse cross sections of RG and wild type stems and leaves. Results illustrated a more pronounced lignin staining in the wild type stem section relative to RG (Figure 4A,C) and vice versa in the leaf (Figure 4B,D). Therefore, histochemical data suggest that stems of the RG mutant have reduced lignin biosynthesis whereas the leaves display increased levels. Transcriptional characterization of 4-week old RG and WT stems demonstrated a down-regulation for key genes involved in the lignin pathway for RG compared to the wild type, corroborating the histochemical evidence for lignin reduction (Figure 3B). One exception was CAD, whose expression was up-regulated, contradictory to reduced lignification of this tissue.

Bottom Line: Reduced lignin was linked to improved saccharification in RG stems, but a chemical shift to greater S:G ratios in RG stem lignin was also observed.Antithetic lignin accumulation was observed in the RG mutant leaf-and stem-tissue, which resulted in greater saccharification efficiency in the RG stem and differential thermochemical product yield in high lignin leaves.Thus, the red leaf coloration of the RG mutant represents a potential marker for improved conversion of stem cellulose to fermentable sugars in the C4 grass Sorghum.

View Article: PubMed Central - HTML - PubMed

Affiliation: Plant Physiology, Department of Horticulture, Agricultural Science Center North, University of Kentucky, Lexington, KY 40546, USA. sdebo2@uky.edu.

ABSTRACT

Background: Improving saccharification efficiency in bioenergy crop species remains an important challenge. Here, we report the characterization of a Sorghum (Sorghum bicolor L.) mutant, named REDforGREEN (RG), as a bioenergy feedstock.

Results: It was found that RG displayed increased accumulation of lignin in leaves and depletion in the stems, antithetic to the trend observed in wild type. Consistent with these measurements, the RG leaf tissue displayed reduced saccharification efficiency whereas the stem saccharification efficiency increased relative to wild type. Reduced lignin was linked to improved saccharification in RG stems, but a chemical shift to greater S:G ratios in RG stem lignin was also observed. Similarities in cellulose content and structure by XRD-analysis support the correlation between increased saccharification properties and reduced lignin instead of changes in the cellulose composition and/or structure.

Conclusion: Antithetic lignin accumulation was observed in the RG mutant leaf-and stem-tissue, which resulted in greater saccharification efficiency in the RG stem and differential thermochemical product yield in high lignin leaves. Thus, the red leaf coloration of the RG mutant represents a potential marker for improved conversion of stem cellulose to fermentable sugars in the C4 grass Sorghum.

No MeSH data available.


Related in: MedlinePlus