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Conifer R2R3-MYB transcription factors: sequence analyses and gene expression in wood-forming tissues of white spruce (Picea glauca).

Bedon F, Grima-Pettenati J, Mackay J - BMC Plant Biol. (2007)

Bottom Line: The number and length of the introns in spruce MYB genes varied significantly, but their positions were well conserved relative to angiosperm MYB genes.Our survey of 18 conifer R2R3-MYB genes clearly showed a gene family structure similar to that of Arabidopsis.Three of the sequences are likely to play a role in lignin metabolism and/or wood formation in gymnosperm trees, including a close homolog of the loblolly pine PtMYB4, shown to regulate lignin biosynthesis in transgenic tobacco.

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Affiliation: Centre d'étude de la Forêt, Université Laval, Pavillon Charles-Eugène Marchand, Sainte Foy G1K7P4, Québec, Canada. frank.bedon@rsvs.ulaval.ca

ABSTRACT

Background: Several members of the R2R3-MYB family of transcription factors act as regulators of lignin and phenylpropanoid metabolism during wood formation in angiosperm and gymnosperm plants. The angiosperm Arabidopsis has over one hundred R2R3-MYBs genes; however, only a few members of this family have been discovered in gymnosperms.

Results: We isolated and characterised full-length cDNAs encoding R2R3-MYB genes from the gymnosperms white spruce, Picea glauca (13 sequences), and loblolly pine, Pinus taeda L. (five sequences). Sequence similarities and phylogenetic analyses placed the spruce and pine sequences in diverse subgroups of the large R2R3-MYB family, although several of the sequences clustered closely together. We searched the highly variable C-terminal region of diverse plant MYBs for conserved amino acid sequences and identified 20 motifs in the spruce MYBs, nine of which have not previously been reported and three of which are specific to conifers. The number and length of the introns in spruce MYB genes varied significantly, but their positions were well conserved relative to angiosperm MYB genes. Quantitative RTPCR of MYB genes transcript abundance in root and stem tissues revealed diverse expression patterns; three MYB genes were preferentially expressed in secondary xylem, whereas others were preferentially expressed in phloem or were ubiquitous. The MYB genes expressed in xylem, and three others, were up-regulated in the compression wood of leaning trees within 76 hours of induction.

Conclusion: Our survey of 18 conifer R2R3-MYB genes clearly showed a gene family structure similar to that of Arabidopsis. Three of the sequences are likely to play a role in lignin metabolism and/or wood formation in gymnosperm trees, including a close homolog of the loblolly pine PtMYB4, shown to regulate lignin biosynthesis in transgenic tobacco.

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Transcript abundance for 13 spruce MYB genes and 4CL in various organs and tissues. Transcript abundance was determined by Q-RTPCR of six tissues from two different 33-year-old trees (number of molecules per ng of total RNA, see methods). The transcript level of an elongation factor (EF1-α) gene was used as an RNA control. N, needles; Stem tissues: P, periderm; Ph, differentiating phloem; X, differentiating xylem; Root tissues: PPh, root periderm with differentiating phloem; X, root differentiating xylem. Data are based on three technical repetitions per tree, i.e. six measurements per data point. Vertical bars represent the standard error. 4CL: 4-coumarate: CoA ligase. NS, no PCR product detected.
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Figure 3: Transcript abundance for 13 spruce MYB genes and 4CL in various organs and tissues. Transcript abundance was determined by Q-RTPCR of six tissues from two different 33-year-old trees (number of molecules per ng of total RNA, see methods). The transcript level of an elongation factor (EF1-α) gene was used as an RNA control. N, needles; Stem tissues: P, periderm; Ph, differentiating phloem; X, differentiating xylem; Root tissues: PPh, root periderm with differentiating phloem; X, root differentiating xylem. Data are based on three technical repetitions per tree, i.e. six measurements per data point. Vertical bars represent the standard error. 4CL: 4-coumarate: CoA ligase. NS, no PCR product detected.

Mentions: We surveyed the abundance of each of the 13 PgMYB gene transcripts by Q-RTPCR, in mature (33-year-old trees) and young (3-year-old) green-house-grown trees to determine their tissue distribution during normal development. Six different organs and differentiating tissues (the young needles; the periderm, phloem and xylem from the stems; and the periderm with phloem, or bark, and xylem from the roots) were collected from two different mature trees (Fig. 3). For tissue comparisons, we calculated the number initial MYB RNA molecules per ng of total RNA. Spruce PgMYBs 2, 4 and 8 were expressed preferentially in differentiating xylem from stem and root. Other MYBs were abundant in the needles along with one to two other tissues from the stem or the roots or both, Some MYB mRNAs also appeared to have rather ubiquitous profiles or low abundance transcripts. The RNA abundance of lignin biosynthesis enzymes PAL, 4CL, CCoAOMT and CAD were also determined in the same tissue samples. The lignin enzymes RNAs all gave very similar profiles, and they were most abundant in differentiating xylem (only 4CL is shown; Fig. 3).


Conifer R2R3-MYB transcription factors: sequence analyses and gene expression in wood-forming tissues of white spruce (Picea glauca).

Bedon F, Grima-Pettenati J, Mackay J - BMC Plant Biol. (2007)

Transcript abundance for 13 spruce MYB genes and 4CL in various organs and tissues. Transcript abundance was determined by Q-RTPCR of six tissues from two different 33-year-old trees (number of molecules per ng of total RNA, see methods). The transcript level of an elongation factor (EF1-α) gene was used as an RNA control. N, needles; Stem tissues: P, periderm; Ph, differentiating phloem; X, differentiating xylem; Root tissues: PPh, root periderm with differentiating phloem; X, root differentiating xylem. Data are based on three technical repetitions per tree, i.e. six measurements per data point. Vertical bars represent the standard error. 4CL: 4-coumarate: CoA ligase. NS, no PCR product detected.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 3: Transcript abundance for 13 spruce MYB genes and 4CL in various organs and tissues. Transcript abundance was determined by Q-RTPCR of six tissues from two different 33-year-old trees (number of molecules per ng of total RNA, see methods). The transcript level of an elongation factor (EF1-α) gene was used as an RNA control. N, needles; Stem tissues: P, periderm; Ph, differentiating phloem; X, differentiating xylem; Root tissues: PPh, root periderm with differentiating phloem; X, root differentiating xylem. Data are based on three technical repetitions per tree, i.e. six measurements per data point. Vertical bars represent the standard error. 4CL: 4-coumarate: CoA ligase. NS, no PCR product detected.
Mentions: We surveyed the abundance of each of the 13 PgMYB gene transcripts by Q-RTPCR, in mature (33-year-old trees) and young (3-year-old) green-house-grown trees to determine their tissue distribution during normal development. Six different organs and differentiating tissues (the young needles; the periderm, phloem and xylem from the stems; and the periderm with phloem, or bark, and xylem from the roots) were collected from two different mature trees (Fig. 3). For tissue comparisons, we calculated the number initial MYB RNA molecules per ng of total RNA. Spruce PgMYBs 2, 4 and 8 were expressed preferentially in differentiating xylem from stem and root. Other MYBs were abundant in the needles along with one to two other tissues from the stem or the roots or both, Some MYB mRNAs also appeared to have rather ubiquitous profiles or low abundance transcripts. The RNA abundance of lignin biosynthesis enzymes PAL, 4CL, CCoAOMT and CAD were also determined in the same tissue samples. The lignin enzymes RNAs all gave very similar profiles, and they were most abundant in differentiating xylem (only 4CL is shown; Fig. 3).

Bottom Line: The number and length of the introns in spruce MYB genes varied significantly, but their positions were well conserved relative to angiosperm MYB genes.Our survey of 18 conifer R2R3-MYB genes clearly showed a gene family structure similar to that of Arabidopsis.Three of the sequences are likely to play a role in lignin metabolism and/or wood formation in gymnosperm trees, including a close homolog of the loblolly pine PtMYB4, shown to regulate lignin biosynthesis in transgenic tobacco.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre d'étude de la Forêt, Université Laval, Pavillon Charles-Eugène Marchand, Sainte Foy G1K7P4, Québec, Canada. frank.bedon@rsvs.ulaval.ca

ABSTRACT

Background: Several members of the R2R3-MYB family of transcription factors act as regulators of lignin and phenylpropanoid metabolism during wood formation in angiosperm and gymnosperm plants. The angiosperm Arabidopsis has over one hundred R2R3-MYBs genes; however, only a few members of this family have been discovered in gymnosperms.

Results: We isolated and characterised full-length cDNAs encoding R2R3-MYB genes from the gymnosperms white spruce, Picea glauca (13 sequences), and loblolly pine, Pinus taeda L. (five sequences). Sequence similarities and phylogenetic analyses placed the spruce and pine sequences in diverse subgroups of the large R2R3-MYB family, although several of the sequences clustered closely together. We searched the highly variable C-terminal region of diverse plant MYBs for conserved amino acid sequences and identified 20 motifs in the spruce MYBs, nine of which have not previously been reported and three of which are specific to conifers. The number and length of the introns in spruce MYB genes varied significantly, but their positions were well conserved relative to angiosperm MYB genes. Quantitative RTPCR of MYB genes transcript abundance in root and stem tissues revealed diverse expression patterns; three MYB genes were preferentially expressed in secondary xylem, whereas others were preferentially expressed in phloem or were ubiquitous. The MYB genes expressed in xylem, and three others, were up-regulated in the compression wood of leaning trees within 76 hours of induction.

Conclusion: Our survey of 18 conifer R2R3-MYB genes clearly showed a gene family structure similar to that of Arabidopsis. Three of the sequences are likely to play a role in lignin metabolism and/or wood formation in gymnosperm trees, including a close homolog of the loblolly pine PtMYB4, shown to regulate lignin biosynthesis in transgenic tobacco.

Show MeSH