Although poplar is widely used for genomic and biotechnological manipulations of wood, the cellular basis of wood development in poplar has not been accurately documented at an ultrastructural level. Developing second...Although poplar is widely used for genomic and biotechnological manipulations of wood, the cellular basis of wood development in poplar has not been accurately documented at an ultrastructural level. Developing secondary xylem cells from hybrid poplar （Populus deltoides x P. trichocarpa）, which were actively making secondary cell walls, were preserved with high pressure freezing/freeze substitution for light and electron microscopy. The distribution of xylans and mannans in the different cell types of developing secondary xylem were detected with immunofluorescence and immuno-gold labeling. While xylans, detected with the monoclonal antibody LM10, had a general distribution across the secondary xylem, mannans were enriched in the S2 secondary cell wall layer of fibers. To observe the cellular structures associated with secondary wall production, cryofixed fibers were examined with transmission electron microscopy during differentiation. There were abundant cortical microtubules and endomembrane activity in cells during the intense phase of secondary cell wall synthesis. Microtubuleassociated small membrane compartments were commonly observed, as well as Golgi and secretory vesicles fusing with the plasma membrane.展开更多
Genetic manipulation of cellulose biosynthesis in trees may provide novel insights into the growth and development of trees. To explore this possibility, the overexpression of an aspen secondary wall-associated cellul...Genetic manipulation of cellulose biosynthesis in trees may provide novel insights into the growth and development of trees. To explore this possibility, the overexpression of an aspen secondary wall-associated cellulose synthase （PtdCesAS） gene was attempted in transgenic aspen （Populus tremuloides L.） and unexpectedly resulted in silencing of the transgene as well as its endogenous counterparts. The main axis of the transgenic aspen plants quickly stopped growing, and weak branches adopted a weeping growth habit. Furthermore, transgenic plants initially developed smaller leaves and a less extensive root system. Secondary xylem （wood） of transgenic aspen plants contained as little as 10% cellulose normalized to dry weight compared to 41% cellulose typically found in normal aspen wood. This massive reduction in cellulose was accompanied by proportional increases in lignin （35%） and non-cellulosic polysaccharides （55%） compared to the 22% lignin and 36% non-cellulosic polysaccharides in control plants. The transgenic stems pro- duced typical collapsed or ＇irregular＇ xylem vessels that had altered secondary wall morphology and contained greatly reduced amounts of crystalline cellulose. These results demonstrate the fundamental role of secondary wall cellulose within the secondary xylem in maintaining the strength and structural integrity required to establish the vertical growth habit in trees.展开更多
Secondary xylem development has long been recognized as a typical case of programmed cell death （PCD） in plants. During PCD, the degradation of genomic DNA is catalyzed by endonucleases. However, to date, no endonuc...Secondary xylem development has long been recognized as a typical case of programmed cell death （PCD） in plants. During PCD, the degradation of genomic DNA is catalyzed by endonucleases. However, to date, no endonuclease has been shown to participate in secondary xylem development. Two novel Ca^2＋-dependent DNase genes, EuCaN1 and EuCaN2, were identified from the differentiating secondary xylem of the tree Eucommia ulmoides Oliv., their functions were studied by DNase activity assay, in situ hybridization, protein immunolocalization and virus-induced gene silencing experiments. Full-length cDNAs of EuCaN1 and EuCaN2 contained an open reading frame of 987 bp, encoding two proteins of 328 amino acids with SNase-like functional domains. The genomic DNA sequence for EuCaN1 had no introns, while EuCaN2 had 8 introns. EuCaN1 and EuCaN2 digested ssDNA and dsDNA with Ca^2＋-dependence at neutral pH. Their expression was confined to differentiating secondary xylem cells and the proteins were localized in the nucleus. Their activity dynamics was closely correlated with secondary xylem development. Secondary xylem cell differentiation is influenced by RNAi of endonuclease genes. The results provide evidence that the Ca^2＋-dependent DNases are involved in secondary xylem development.展开更多
A key question in the secondary growth of trees is how differentiation of the vascular cambium cells is directed to concurrently form two different tissues： xylem or phloem, class III homeodomain-leucine zipper （HD-...A key question in the secondary growth of trees is how differentiation of the vascular cambium cells is directed to concurrently form two different tissues： xylem or phloem, class III homeodomain-leucine zipper （HD-Zip III） genes are known to play critical roles in the initiation, patterning, and differentiation of the vascular system in the process of primary and secondary growth. However, the mechanism of how these genes control secondary vascular dif- ferentiation is unknown. Here, we show that a Populus class III HD-Zip gene, PtrHB7, was preferentially expressed in cambial zone. PtrHB7-suppressed plants displayed significant changes in vascular tissues with a reduction in xylem but increase in phloem. Transcriptional analysis revealed that genes regulating xylem differentiation were down-regulated, whereas genes regulating phloem differentiation were up-regulated. Correspondingly, PtrHB7 overexpression enhanced differentiation of cambial cells toward xylem cells but inhibited phloem differentiation. PtrHB7 regulation on cambial cell differentiation was associated with its transcript abundance. Together, the results demonstrated that PtrHB7 plays a critical role in controlling a balanced differentiation between secondary xylem and phloem tissues in the process of Populus secondary growth in a dosage-dependent manner.展开更多
基金Supported by the Natural Sciences and Engineering Research Council of Canada, Discovery Grant to LS
文摘Although poplar is widely used for genomic and biotechnological manipulations of wood, the cellular basis of wood development in poplar has not been accurately documented at an ultrastructural level. Developing secondary xylem cells from hybrid poplar （Populus deltoides x P. trichocarpa）, which were actively making secondary cell walls, were preserved with high pressure freezing/freeze substitution for light and electron microscopy. The distribution of xylans and mannans in the different cell types of developing secondary xylem were detected with immunofluorescence and immuno-gold labeling. While xylans, detected with the monoclonal antibody LM10, had a general distribution across the secondary xylem, mannans were enriched in the S2 secondary cell wall layer of fibers. To observe the cellular structures associated with secondary wall production, cryofixed fibers were examined with transmission electron microscopy during differentiation. There were abundant cortical microtubules and endomembrane activity in cells during the intense phase of secondary cell wall synthesis. Microtubuleassociated small membrane compartments were commonly observed, as well as Golgi and secretory vesicles fusing with the plasma membrane.
文摘Genetic manipulation of cellulose biosynthesis in trees may provide novel insights into the growth and development of trees. To explore this possibility, the overexpression of an aspen secondary wall-associated cellulose synthase （PtdCesAS） gene was attempted in transgenic aspen （Populus tremuloides L.） and unexpectedly resulted in silencing of the transgene as well as its endogenous counterparts. The main axis of the transgenic aspen plants quickly stopped growing, and weak branches adopted a weeping growth habit. Furthermore, transgenic plants initially developed smaller leaves and a less extensive root system. Secondary xylem （wood） of transgenic aspen plants contained as little as 10% cellulose normalized to dry weight compared to 41% cellulose typically found in normal aspen wood. This massive reduction in cellulose was accompanied by proportional increases in lignin （35%） and non-cellulosic polysaccharides （55%） compared to the 22% lignin and 36% non-cellulosic polysaccharides in control plants. The transgenic stems pro- duced typical collapsed or ＇irregular＇ xylem vessels that had altered secondary wall morphology and contained greatly reduced amounts of crystalline cellulose. These results demonstrate the fundamental role of secondary wall cellulose within the secondary xylem in maintaining the strength and structural integrity required to establish the vertical growth habit in trees.
基金supported by the National Basic Research Program of China (2012CB114500)the National Natural Science Foundation of China (31070156)
文摘Secondary xylem development has long been recognized as a typical case of programmed cell death （PCD） in plants. During PCD, the degradation of genomic DNA is catalyzed by endonucleases. However, to date, no endonuclease has been shown to participate in secondary xylem development. Two novel Ca^2＋-dependent DNase genes, EuCaN1 and EuCaN2, were identified from the differentiating secondary xylem of the tree Eucommia ulmoides Oliv., their functions were studied by DNase activity assay, in situ hybridization, protein immunolocalization and virus-induced gene silencing experiments. Full-length cDNAs of EuCaN1 and EuCaN2 contained an open reading frame of 987 bp, encoding two proteins of 328 amino acids with SNase-like functional domains. The genomic DNA sequence for EuCaN1 had no introns, while EuCaN2 had 8 introns. EuCaN1 and EuCaN2 digested ssDNA and dsDNA with Ca^2＋-dependence at neutral pH. Their expression was confined to differentiating secondary xylem cells and the proteins were localized in the nucleus. Their activity dynamics was closely correlated with secondary xylem development. Secondary xylem cell differentiation is influenced by RNAi of endonuclease genes. The results provide evidence that the Ca^2＋-dependent DNases are involved in secondary xylem development.
基金This research was supported by the National Key Basic Research Program of China，the National Natural Science Foundation of China (31130012) to L..L.,and the National Natural Science Foundation of China (30972329) to X.W
文摘A key question in the secondary growth of trees is how differentiation of the vascular cambium cells is directed to concurrently form two different tissues： xylem or phloem, class III homeodomain-leucine zipper （HD-Zip III） genes are known to play critical roles in the initiation, patterning, and differentiation of the vascular system in the process of primary and secondary growth. However, the mechanism of how these genes control secondary vascular dif- ferentiation is unknown. Here, we show that a Populus class III HD-Zip gene, PtrHB7, was preferentially expressed in cambial zone. PtrHB7-suppressed plants displayed significant changes in vascular tissues with a reduction in xylem but increase in phloem. Transcriptional analysis revealed that genes regulating xylem differentiation were down-regulated, whereas genes regulating phloem differentiation were up-regulated. Correspondingly, PtrHB7 overexpression enhanced differentiation of cambial cells toward xylem cells but inhibited phloem differentiation. PtrHB7 regulation on cambial cell differentiation was associated with its transcript abundance. Together, the results demonstrated that PtrHB7 plays a critical role in controlling a balanced differentiation between secondary xylem and phloem tissues in the process of Populus secondary growth in a dosage-dependent manner.
