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The Populus Class III HD ZIP transcription factor POPCORONA affects cell differentiation during secondary growth of woody stems.

Du J, Miura E, Robischon M, Martinez C, Groover A - PLoS ONE (2011)

Bottom Line: Synthetic miRNA knock down of POPCORONA results in abnormal lignification in cells of the pith, while overexpression of a miRNA-resistant POPCORONA results in delayed lignification of xylem and phloem fibers during secondary growth.POPCORONA misexpression also results in coordinated changes in expression of genes within a previously described transcriptional network regulating cell differentiation and cell wall biosynthesis, and hormone-related genes associated with fiber differentiation.POPCORONA illustrates another function of Class III HD ZIPs: regulating cell differentiation during secondary growth.

View Article: PubMed Central - PubMed

Affiliation: Institute of Forest Genetics, Pacific Southwest Research Station, U.S. Forest Service, Davis, California, United States of America.

ABSTRACT
The developmental mechanisms regulating cell differentiation and patterning during the secondary growth of woody tissues are poorly understood. Class III HD ZIP transcription factors are evolutionarily ancient and play fundamental roles in various aspects of plant development. Here we investigate the role of a Class III HD ZIP transcription factor, POPCORONA, during secondary growth of woody stems. Transgenic Populus (poplar) trees expressing either a miRNA-resistant POPCORONA or a synthetic miRNA targeting POPCORONA were used to infer function of POPCORONA during secondary growth. Whole plant, histological, and gene expression changes were compared for transgenic and wild-type control plants. Synthetic miRNA knock down of POPCORONA results in abnormal lignification in cells of the pith, while overexpression of a miRNA-resistant POPCORONA results in delayed lignification of xylem and phloem fibers during secondary growth. POPCORONA misexpression also results in coordinated changes in expression of genes within a previously described transcriptional network regulating cell differentiation and cell wall biosynthesis, and hormone-related genes associated with fiber differentiation. POPCORONA illustrates another function of Class III HD ZIPs: regulating cell differentiation during secondary growth.

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Quantification of phenotypes in bottom internode of 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN knockdown transgenics.(a) Comparison of number of phloem fibers in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. (b) Comparison of number of lignified xylem cell layers in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. (c) Comparison of number of lignified pith cells in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. Relative expression levels (mean ± SE) were calculated from three cross-sections of the bottom internodes of three independent wild type plants, three miRNAd gain of function transgenics, three 35S::PCN-miRNAd transgenics prepared from different batches of two month-old plants.
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pone-0017458-g007: Quantification of phenotypes in bottom internode of 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN knockdown transgenics.(a) Comparison of number of phloem fibers in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. (b) Comparison of number of lignified xylem cell layers in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. (c) Comparison of number of lignified pith cells in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. Relative expression levels (mean ± SE) were calculated from three cross-sections of the bottom internodes of three independent wild type plants, three miRNAd gain of function transgenics, three 35S::PCN-miRNAd transgenics prepared from different batches of two month-old plants.

Mentions: As mentioned, 35S::miRNA-PCN plants had only a modest reduction in PCN transcript abundance (Fig. 4), and no whole plant phenotype was apparent (Fig. 5). However, cross sections revealed subtle defects in stem development. At the fourth internode from the apex, lignified phloem fibers are already apparent in 35S::miRNA-PCN plants, while they are lacking at this stage of development in the wild-type (Fig. 6I). Also at this position, cambium activity is evident as cell files within the cambial zone, and modest amounts of secondary xylem have formed. By internode seven, 35S::miRNA-PCN plants have more abundant secondary and noticeably more highly lignified phloem fibers than the wild-type (Fig. 6j). Sections through the bottom of the stem are similar to the wild-type, except that there is abnormal lignification of some cells within the pith (Fig. 6 k,l). These abnormally lignified cells are primarily found adjacent to the position of primary vascular bundles (Fig. 6k,l). In summary, misexpression or down-regulation of PCN results in differences in the number of phloem fibers, number of xylem cell layers, and number of lignified pith cells, as quantified in Fig. 7.


The Populus Class III HD ZIP transcription factor POPCORONA affects cell differentiation during secondary growth of woody stems.

Du J, Miura E, Robischon M, Martinez C, Groover A - PLoS ONE (2011)

Quantification of phenotypes in bottom internode of 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN knockdown transgenics.(a) Comparison of number of phloem fibers in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. (b) Comparison of number of lignified xylem cell layers in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. (c) Comparison of number of lignified pith cells in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. Relative expression levels (mean ± SE) were calculated from three cross-sections of the bottom internodes of three independent wild type plants, three miRNAd gain of function transgenics, three 35S::PCN-miRNAd transgenics prepared from different batches of two month-old plants.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3046250&req=5

pone-0017458-g007: Quantification of phenotypes in bottom internode of 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN knockdown transgenics.(a) Comparison of number of phloem fibers in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. (b) Comparison of number of lignified xylem cell layers in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. (c) Comparison of number of lignified pith cells in the bottom internodes of wild-type, 35S::PCN-miRNAd gain of function and 35S::miRNA-PCN. Relative expression levels (mean ± SE) were calculated from three cross-sections of the bottom internodes of three independent wild type plants, three miRNAd gain of function transgenics, three 35S::PCN-miRNAd transgenics prepared from different batches of two month-old plants.
Mentions: As mentioned, 35S::miRNA-PCN plants had only a modest reduction in PCN transcript abundance (Fig. 4), and no whole plant phenotype was apparent (Fig. 5). However, cross sections revealed subtle defects in stem development. At the fourth internode from the apex, lignified phloem fibers are already apparent in 35S::miRNA-PCN plants, while they are lacking at this stage of development in the wild-type (Fig. 6I). Also at this position, cambium activity is evident as cell files within the cambial zone, and modest amounts of secondary xylem have formed. By internode seven, 35S::miRNA-PCN plants have more abundant secondary and noticeably more highly lignified phloem fibers than the wild-type (Fig. 6j). Sections through the bottom of the stem are similar to the wild-type, except that there is abnormal lignification of some cells within the pith (Fig. 6 k,l). These abnormally lignified cells are primarily found adjacent to the position of primary vascular bundles (Fig. 6k,l). In summary, misexpression or down-regulation of PCN results in differences in the number of phloem fibers, number of xylem cell layers, and number of lignified pith cells, as quantified in Fig. 7.

Bottom Line: Synthetic miRNA knock down of POPCORONA results in abnormal lignification in cells of the pith, while overexpression of a miRNA-resistant POPCORONA results in delayed lignification of xylem and phloem fibers during secondary growth.POPCORONA misexpression also results in coordinated changes in expression of genes within a previously described transcriptional network regulating cell differentiation and cell wall biosynthesis, and hormone-related genes associated with fiber differentiation.POPCORONA illustrates another function of Class III HD ZIPs: regulating cell differentiation during secondary growth.

View Article: PubMed Central - PubMed

Affiliation: Institute of Forest Genetics, Pacific Southwest Research Station, U.S. Forest Service, Davis, California, United States of America.

ABSTRACT
The developmental mechanisms regulating cell differentiation and patterning during the secondary growth of woody tissues are poorly understood. Class III HD ZIP transcription factors are evolutionarily ancient and play fundamental roles in various aspects of plant development. Here we investigate the role of a Class III HD ZIP transcription factor, POPCORONA, during secondary growth of woody stems. Transgenic Populus (poplar) trees expressing either a miRNA-resistant POPCORONA or a synthetic miRNA targeting POPCORONA were used to infer function of POPCORONA during secondary growth. Whole plant, histological, and gene expression changes were compared for transgenic and wild-type control plants. Synthetic miRNA knock down of POPCORONA results in abnormal lignification in cells of the pith, while overexpression of a miRNA-resistant POPCORONA results in delayed lignification of xylem and phloem fibers during secondary growth. POPCORONA misexpression also results in coordinated changes in expression of genes within a previously described transcriptional network regulating cell differentiation and cell wall biosynthesis, and hormone-related genes associated with fiber differentiation. POPCORONA illustrates another function of Class III HD ZIPs: regulating cell differentiation during secondary growth.

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