Plant cell walls play a central role in cell growth and morphogenesis. All plant cells have a primary wall. The formation of a secondary cell wall is restricted to particular cell types, such as the xylem cells, highly lignified cells that provide support and transport functions to the plant. The mechanisms regulating secondary cell wall biogenesis remain largely unknown. To identify genes involved in such mechanisms, a genetic screen for mutants with altered xylem development in the primary root of Arabidopsis thaliana has been conducted. Three different classes of mutants were identified. They are characterised by increased number of xylem strands (m"), altered timing of protoxylem differentiation (tpx) and ectopic lignification (eh). Initial characterisation of the mutant phenotypes, establishment of different complementation groups and their map position in the Arabidopsis genome has been determined. Mutations in the EL [I locus have been characterised in further detail. The eli l mutants exhibited ectopic lignification of cells throughout the plant that never normally lignify. Xylem cells in elil were misshapen and failed to differentiate into continuous strands, causing a disorganised xylem. elil mutants also exhibited altered cell expansion resulting in a stunted phenotype. Abnormal distribution of cellulose and lignin was observed in elil cell walls. Ultrastructural analysis of elil cell walls using an anti-lignin antibody has revealed that that the ectopic deposition of lignin-like compounds occurs within an altered secondary wall. Furthermore, other previously described cell expansion mutants, such as lit, rswl (at the conditional temperature) and det3, exhibited lignification patterns reminiscent to that of elil mutants. Analysis of the genetic interactions of elil with the lit mutant revealed that ELlI and LIT genes act in independent pathways to control cell expansion. These results, together with the double mutant analysis of eli l with other cell expansion mutants suggested a link between cell growth and differentiation of secondary thickened walls. Map-based cloning placed the ELJ1 gene in a 140-Kb interval on the top arm of Arabidopsis chromosome V. A candidate gene approach was used that identified a gene encoding a cellulose synthase catalytic subunit (CesA), AthCesA-3 as a candidate. Sequence analysis revealed that the AthCesA-3 gene is mutated in two elil alleles sequenced, both mutations leading to amino acid substitutions. Initial complementation experiments of elil plants with the wild type AthCesA-3 gene appeared to restore the wild type phenotype, suggesting that mutations in the AthCesA-3 gene gave rise to the elil phenotypes. These studies represent an important contribution to our understanding of the molecular mechanism of cellulose deposition during cell expansion and secondary cell wall deposition during plant morphogenesis.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:365009 |
| Date | January 2000 |
| Creators | Cano Delgado, Ana Isabel |
| Publisher | University of East Anglia |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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