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Gene expression analysis of flax seed development.

Venglat P, Xiang D, Qiu S, Stone SL, Tibiche C, Cram D, Alting-Mees M, Nowak J, Cloutier S, Deyholos M, Bekkaoui F, Sharpe A, Wang E, Rowland G, Selvaraj G, Datla R - BMC Plant Biol. (2011)

Bottom Line: When compared with fully sequenced plant genomes, the flax unigenes resembled poplar and castor bean more than grape, sorghum, rice or Arabidopsis.We have developed a foundational database of expressed sequences and collection of plasmid clones that comprise even low-expressed genes such as those encoding transcription factors.Flax belongs to a taxonomic group of diverse plants and the large sequence database will allow for evolutionary studies as well.

View Article: PubMed Central - HTML - PubMed

Affiliation: Plant Biotechnology Institute, NRC, 110 Gymnasium Place, Saskatoon, Saskatchewan, S7N 0W9, Canada.

ABSTRACT

Background: Flax, Linum usitatissimum L., is an important crop whose seed oil and stem fiber have multiple industrial applications. Flax seeds are also well-known for their nutritional attributes, viz., omega-3 fatty acids in the oil and lignans and mucilage from the seed coat. In spite of the importance of this crop, there are few molecular resources that can be utilized toward improving seed traits. Here, we describe flax embryo and seed development and generation of comprehensive genomic resources for the flax seed.

Results: We describe a large-scale generation and analysis of expressed sequences in various tissues. Collectively, the 13 libraries we have used provide a broad representation of genes active in developing embryos (globular, heart, torpedo, cotyledon and mature stages) seed coats (globular and torpedo stages) and endosperm (pooled globular to torpedo stages) and genes expressed in flowers, etiolated seedlings, leaves, and stem tissue. A total of 261,272 expressed sequence tags (EST) (GenBank accessions LIBEST_026995 to LIBEST_027011) were generated. These EST libraries included transcription factor genes that are typically expressed at low levels, indicating that the depth is adequate for in silico expression analysis. Assembly of the ESTs resulted in 30,640 unigenes and 82% of these could be identified on the basis of homology to known and hypothetical genes from other plants. When compared with fully sequenced plant genomes, the flax unigenes resembled poplar and castor bean more than grape, sorghum, rice or Arabidopsis. Nearly one-fifth of these (5,152) had no homologs in sequences reported for any organism, suggesting that this category represents genes that are likely unique to flax. Digital analyses revealed gene expression dynamics for the biosynthesis of a number of important seed constituents during seed development.

Conclusions: We have developed a foundational database of expressed sequences and collection of plasmid clones that comprise even low-expressed genes such as those encoding transcription factors. This has allowed us to delineate the spatio-temporal aspects of gene expression underlying the biosynthesis of a number of important seed constituents in flax. Flax belongs to a taxonomic group of diverse plants and the large sequence database will allow for evolutionary studies as well.

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Flax embryo development. (A) Cleared seed soon after fertilization. The embryo sac (arrow) encloses the embryo and endosperm and is anchored in the micropylar end (me) of the thick seed coat. (B-O) Scanning electron microscopy of developing flax embryo. (B) Dissected micropylar end of the seed showing endosperm cells (en) surrounding the developing globular embryo (em). (C) Globular embryo with suspensor anchored at the micropylar end. (D) Micropylar sleeve that remains after removal of the globular embryonic suspensor. (E) Globular embryo. (F) Heart embryo. The cotyledon primordia are indicated by "cp". (G) Early torpedo embryo. (H) Late torpedo embryos with pointed cotyledon tips. (I) Cotyledon stage embryo with rounded cotyledon tips. (J) Mature embryo with elongated cotyledons and a short embryonic axis. (K) Higher magnification of the cotyledon (co) and hypocotyl (hy) as indicated by the inset rectangle shown in (J). (L) The radicle tip showing the embryonic root apical meristem (ram). (M) The embryonic shoot apical meristem (sam) and leaf primordia (lp). Mature embryonic (N) cotyledon and (O) hypocotyl in cross-section to show cellular differentiation and storage deposits. Bar = 1 mm (J), 0.1 mm (A, B, G-I, K-O) and 10 μm (C-F).
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Figure 1: Flax embryo development. (A) Cleared seed soon after fertilization. The embryo sac (arrow) encloses the embryo and endosperm and is anchored in the micropylar end (me) of the thick seed coat. (B-O) Scanning electron microscopy of developing flax embryo. (B) Dissected micropylar end of the seed showing endosperm cells (en) surrounding the developing globular embryo (em). (C) Globular embryo with suspensor anchored at the micropylar end. (D) Micropylar sleeve that remains after removal of the globular embryonic suspensor. (E) Globular embryo. (F) Heart embryo. The cotyledon primordia are indicated by "cp". (G) Early torpedo embryo. (H) Late torpedo embryos with pointed cotyledon tips. (I) Cotyledon stage embryo with rounded cotyledon tips. (J) Mature embryo with elongated cotyledons and a short embryonic axis. (K) Higher magnification of the cotyledon (co) and hypocotyl (hy) as indicated by the inset rectangle shown in (J). (L) The radicle tip showing the embryonic root apical meristem (ram). (M) The embryonic shoot apical meristem (sam) and leaf primordia (lp). Mature embryonic (N) cotyledon and (O) hypocotyl in cross-section to show cellular differentiation and storage deposits. Bar = 1 mm (J), 0.1 mm (A, B, G-I, K-O) and 10 μm (C-F).

Mentions: Limited information is available regarding flax seed development, despite its economic importance. Since the seed is an economically important output of this crop, in this study, we performed a detailed analysis of embryogenesis and flax seed development. The flax seed consists of three major tissues: the diploid embryo and triploid endosperm as products of double fertilization, and the maternal seed coat tissue. Soon after fertilization, the seed is translucent and the embryo sac is upright within the integuments (Figure 1A). The developing embryo is anchored at the micropylar end of the embryo sac. The thick, clear and fragile integuments of the fertilized ovule differentiate into the thin, dark and protective seed coat during seed development. Observation during the dissection process revealed that the endosperm initials, which formed at fertilization, undergo divisions to form a cellularized endosperm by the globular embryo stage (Figure 1B and Figure 2H). The endosperm progressively increases in size up to the torpedo stage, after which time it begins to degenerate, presumably to make space for the rapidly elongating cotyledons and to provide nutritional support to the developing embryo. By the late cotyledon stage the majority of endosperm cells have been consumed, leaving a thin layer of endosperm on the inner wall of the seed coat of the maturing seed.


Gene expression analysis of flax seed development.

Venglat P, Xiang D, Qiu S, Stone SL, Tibiche C, Cram D, Alting-Mees M, Nowak J, Cloutier S, Deyholos M, Bekkaoui F, Sharpe A, Wang E, Rowland G, Selvaraj G, Datla R - BMC Plant Biol. (2011)

Flax embryo development. (A) Cleared seed soon after fertilization. The embryo sac (arrow) encloses the embryo and endosperm and is anchored in the micropylar end (me) of the thick seed coat. (B-O) Scanning electron microscopy of developing flax embryo. (B) Dissected micropylar end of the seed showing endosperm cells (en) surrounding the developing globular embryo (em). (C) Globular embryo with suspensor anchored at the micropylar end. (D) Micropylar sleeve that remains after removal of the globular embryonic suspensor. (E) Globular embryo. (F) Heart embryo. The cotyledon primordia are indicated by "cp". (G) Early torpedo embryo. (H) Late torpedo embryos with pointed cotyledon tips. (I) Cotyledon stage embryo with rounded cotyledon tips. (J) Mature embryo with elongated cotyledons and a short embryonic axis. (K) Higher magnification of the cotyledon (co) and hypocotyl (hy) as indicated by the inset rectangle shown in (J). (L) The radicle tip showing the embryonic root apical meristem (ram). (M) The embryonic shoot apical meristem (sam) and leaf primordia (lp). Mature embryonic (N) cotyledon and (O) hypocotyl in cross-section to show cellular differentiation and storage deposits. Bar = 1 mm (J), 0.1 mm (A, B, G-I, K-O) and 10 μm (C-F).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 1: Flax embryo development. (A) Cleared seed soon after fertilization. The embryo sac (arrow) encloses the embryo and endosperm and is anchored in the micropylar end (me) of the thick seed coat. (B-O) Scanning electron microscopy of developing flax embryo. (B) Dissected micropylar end of the seed showing endosperm cells (en) surrounding the developing globular embryo (em). (C) Globular embryo with suspensor anchored at the micropylar end. (D) Micropylar sleeve that remains after removal of the globular embryonic suspensor. (E) Globular embryo. (F) Heart embryo. The cotyledon primordia are indicated by "cp". (G) Early torpedo embryo. (H) Late torpedo embryos with pointed cotyledon tips. (I) Cotyledon stage embryo with rounded cotyledon tips. (J) Mature embryo with elongated cotyledons and a short embryonic axis. (K) Higher magnification of the cotyledon (co) and hypocotyl (hy) as indicated by the inset rectangle shown in (J). (L) The radicle tip showing the embryonic root apical meristem (ram). (M) The embryonic shoot apical meristem (sam) and leaf primordia (lp). Mature embryonic (N) cotyledon and (O) hypocotyl in cross-section to show cellular differentiation and storage deposits. Bar = 1 mm (J), 0.1 mm (A, B, G-I, K-O) and 10 μm (C-F).
Mentions: Limited information is available regarding flax seed development, despite its economic importance. Since the seed is an economically important output of this crop, in this study, we performed a detailed analysis of embryogenesis and flax seed development. The flax seed consists of three major tissues: the diploid embryo and triploid endosperm as products of double fertilization, and the maternal seed coat tissue. Soon after fertilization, the seed is translucent and the embryo sac is upright within the integuments (Figure 1A). The developing embryo is anchored at the micropylar end of the embryo sac. The thick, clear and fragile integuments of the fertilized ovule differentiate into the thin, dark and protective seed coat during seed development. Observation during the dissection process revealed that the endosperm initials, which formed at fertilization, undergo divisions to form a cellularized endosperm by the globular embryo stage (Figure 1B and Figure 2H). The endosperm progressively increases in size up to the torpedo stage, after which time it begins to degenerate, presumably to make space for the rapidly elongating cotyledons and to provide nutritional support to the developing embryo. By the late cotyledon stage the majority of endosperm cells have been consumed, leaving a thin layer of endosperm on the inner wall of the seed coat of the maturing seed.

Bottom Line: When compared with fully sequenced plant genomes, the flax unigenes resembled poplar and castor bean more than grape, sorghum, rice or Arabidopsis.We have developed a foundational database of expressed sequences and collection of plasmid clones that comprise even low-expressed genes such as those encoding transcription factors.Flax belongs to a taxonomic group of diverse plants and the large sequence database will allow for evolutionary studies as well.

View Article: PubMed Central - HTML - PubMed

Affiliation: Plant Biotechnology Institute, NRC, 110 Gymnasium Place, Saskatoon, Saskatchewan, S7N 0W9, Canada.

ABSTRACT

Background: Flax, Linum usitatissimum L., is an important crop whose seed oil and stem fiber have multiple industrial applications. Flax seeds are also well-known for their nutritional attributes, viz., omega-3 fatty acids in the oil and lignans and mucilage from the seed coat. In spite of the importance of this crop, there are few molecular resources that can be utilized toward improving seed traits. Here, we describe flax embryo and seed development and generation of comprehensive genomic resources for the flax seed.

Results: We describe a large-scale generation and analysis of expressed sequences in various tissues. Collectively, the 13 libraries we have used provide a broad representation of genes active in developing embryos (globular, heart, torpedo, cotyledon and mature stages) seed coats (globular and torpedo stages) and endosperm (pooled globular to torpedo stages) and genes expressed in flowers, etiolated seedlings, leaves, and stem tissue. A total of 261,272 expressed sequence tags (EST) (GenBank accessions LIBEST_026995 to LIBEST_027011) were generated. These EST libraries included transcription factor genes that are typically expressed at low levels, indicating that the depth is adequate for in silico expression analysis. Assembly of the ESTs resulted in 30,640 unigenes and 82% of these could be identified on the basis of homology to known and hypothetical genes from other plants. When compared with fully sequenced plant genomes, the flax unigenes resembled poplar and castor bean more than grape, sorghum, rice or Arabidopsis. Nearly one-fifth of these (5,152) had no homologs in sequences reported for any organism, suggesting that this category represents genes that are likely unique to flax. Digital analyses revealed gene expression dynamics for the biosynthesis of a number of important seed constituents during seed development.

Conclusions: We have developed a foundational database of expressed sequences and collection of plasmid clones that comprise even low-expressed genes such as those encoding transcription factors. This has allowed us to delineate the spatio-temporal aspects of gene expression underlying the biosynthesis of a number of important seed constituents in flax. Flax belongs to a taxonomic group of diverse plants and the large sequence database will allow for evolutionary studies as well.

Show MeSH
Related in: MedlinePlus