Biomedical subjects

Neil G Taylor

Publications and source records attributed to Neil G Taylor.

4 recordsLinked to original sources

PubMed2006

Interactions between MUR10/CesA7-dependent secondary cellulose biosynthesis and primary cell wall structure.

Primary cell walls are deposited and remodeled during cell division and expansion. Secondary cell walls are deposited in specialized cells after the expansion phase. It is presently unknown whether and how these processes are interrelated. The Arabidopsis (Arabidopsis thaliana) MUR10 gene is required for normal primary cell wall carbohydrate composition in mature leaves as well as for normal plant growth, hypocotyl strength, and fertility. The overall sugar composition of young mur10 seedlings is not significantly altered; however, the relative proportion of pectin side chains is shifted toward an increase in 1 --> 5-alpha-arabinan relative to 1 --> 4-beta-galactan. mur10 seedlings display reduced fucogalactosylation of tightly cell wall-bound xyloglucan. Expression levels of genes encoding either nucleotide sugar interconversion enzymes or glycosyl transferases, known to be involved in primary and secondary cell wall biosynthesis, are generally unaffected; however, the CesA7 transcript is specifically suppressed in the mur10-1 allele. The MUR10 locus is identical with the CesA7 gene, which encodes a cellulose catalytic subunit previously thought to be specifically involved in secondary cell wall formation. The xylem vessels in young mur10 hypocotyls are collapsed and their birefringence is lost. Moreover, a fucogalactosylated xyloglucan epitope is reduced and a 1 --> 5-alpha-arabinan epitope increased in every cell type in mur10 hypocotyls, including cells that do not deposit secondary walls. mur10 also displays altered distribution of an arabinogalactan-protein epitope previously associated with xylem differentiation and secondary wall thickening. This work indicates the existence of a mechanism that senses secondary cell wall integrity and controls biosynthesis or structural remodeling of primary cell walls and cellular differentiation.

Alleles↗

PubMed2004

The irregular xylem 2 mutant is an allele of korrigan that affects the secondary cell wall of Arabidopsis thaliana.

The irregular xylem 2 (irx2) mutant of Arabidopsis thaliana exhibits a cellulose deficiency in the secondary cell wall, which is brought about by a point mutation in the KORRIGAN (KOR) beta,1-4 endoglucanase (beta,1-4 EGase) gene. Measurement of the total crystalline cellulose in the inflorescence stem indicates that the irx2 mutant contains approximately 30% of the level present in the wild type (WT). Fourier-Transform Infra Red (FTIR) analysis, however, indicates that there is no decrease in cellulose in primary cell walls of the cortical and epidermal cells of the stem. KOR expression is correlated with cellulose synthesis and is highly expressed in cells synthesising a secondary cell wall. Co-precipitation experiments, using either an epitope-tagged form of KOR or IRX3 (AtCesA7), suggest that KOR is not an integral part of the cellulose synthase complex. These data are supported by immunolocalisation of KOR that suggests that KOR does not localise to sites of secondary cell wall deposition in the developing xylem. The defect in irx2 plant is consistent with a role for KOR in the later stages of secondary cell wall formation, suggesting a role in processing of the growing microfibrils or release of the cellulose synthase complex.

Alleles↗

PubMed2003

Interactions among three distinct CesA proteins essential for cellulose synthesis.

In a screen to identify novel cellulose deficient mutants, three lines were shown to be allelic and define a novel complementation group, irregular xylem5 (irx5). IRX5 was cloned and encodes a member of the CesA family of cellulose synthase catalytic subunits (AtCesA4). irx5 plants have an identical phenotype to previously described mutations in two other members of this gene family (IRX1 and IRX3). IRX5, IRX3, and IRX1 are coexpressed in exactly the same cells, and all three proteins interact in detergent solubilized extracts, suggesting that three members of this gene family are required for cellulose synthesis in secondary cell walls. The association of IRX1 and IRX3 was reduced to undetectable levels in the absence of IRX5. Consequently, these data suggest that IRX5, IRX3, and IRX1 are all essential components of the cellulose synthesizing complex and the presence of all three subunits is required for the correct assembly of this complex.

Arabidopsis↗

PubMed2003

Control of cellulose synthase complex localization in developing xylem.

Cellulose synthesis in the developing xylem vessels of Arabidopsis requires three members of the cellulose synthase (CesA) gene family. In young vessels, these three proteins localize within the cell, whereas in older vessels, all three CesA proteins colocalize with bands of cortical microtubules that mark the sites of secondary cell wall deposition. In the absence of one subunit, however, the remaining two subunits are retained in the cell, demonstrating that all three CesA proteins are required to assemble a functional complex. CesA proteins with altered catalytic activity localize normally, suggesting that cellulose synthase activity is not required for this localization. Cortical microtubule arrays are required continually to maintain normal CesA protein localization. By contrast, actin microfilaments do not colocalize with the CesA proteins and are unlikely to play a direct role in their localization. Green fluorescent protein-tagged CesA reveals a novel process in which the structure and/or local environment of the cellulose synthase complex is altered rapidly.

Arabidopsis↗