Microtubules, MAPs and Xylem Formation

Genome-wide identification and expression analysis of GDP-D-mannose pyrophosphorylase and KATANIN in Corymbia citriodora

The GDP-D-mannose pyrophosphorylase (GMP) and microtubule severing enzyme KATANIN (KTN) are crucial for wood formation. Although functional identification has been performed in Arabidopsis, few comprehensive studies have been conducted in forest trees. In this study, we discovered 8 CcGMP and 4 CcKTN genes by analyzing the whole genome sequence of Corymbia citriodora. The chromosomal location, genome synteny, phylogenetic relationship, protein domain, motif identification, gene structure, cis-acting regulatory elements, and protein-interaction of CcGMP and CcKTN were all investigated. KTN has just one pair of segmentally duplicated genes, while GMP has no duplication events. According to gene structure, two 5' UTRs were identified in CcGMP4. Furthermore, there is no protein-interaction between KTN and GMP. Based on real-time PCR, the expression of most genes showed a positive connection with DBH diameters. In addition, the expression of CcGMP4 and CcKTN4 genes were greater in different size tree, indicating that these genes are important in secondary xylem production. Overall, this findings will enhance our comprehension of the intricacy of CcGMP&CcKTN across diverse DBHs and furnish valuable insights for future functional characterization of specific genes in C. citriodora.

Establishment and Utilization of Habituated Cell Suspension Cultures for Hormone-Inducible Xylogenesis

The development of inducible cell differentiation in suspension cultures led to multiple breakthroughs. It enabled the understanding of the chronology, duration, regulation and interdependency of the multiple events leading to fully functional specialized cells. The most studied cell differentiation in plants using inducible suspension cultures is the formation of tracheary elements (TEs) - the hydro-mineral sap conducting cells. Several in vitro systems established in different plant species have been developed to trigger TE formation on-demand. Here, we describe the establishment, harvesting and analysis of Arabidopsis thaliana stable habituated cell lines inducible by hormones to differentiate into TEs on-demand. Moreover, we explain the means to monitor and modify the chronology, duration and regulation of the progression of TE formation.

The cell biology of lignification in higher plants

BACKGROUND

Lignin is a polyphenolic polymer that strengthens and waterproofs the cell wall of specialized plant cell types. Lignification is part of the normal differentiation programme and functioning of specific cell types, but can also be triggered as a response to various biotic and abiotic stresses in cells that would not otherwise be lignifying.

SCOPE

Cell wall lignification exhibits specific characteristics depending on the cell type being considered. These characteristics include the timing of lignification during cell differentiation, the palette of associated enzymes and substrates, the sub-cellular deposition sites, the monomeric composition and the cellular autonomy for lignin monomer production. This review provides an overview of the current understanding of lignin biosynthesis and polymerization at the cell biology level.

CONCLUSIONS

The lignification process ranges from full autonomy to complete co-operation depending on the cell type. The different roles of lignin for the function of each specific plant cell type are clearly illustrated by the multiple phenotypic defects exhibited by knock-out mutants in lignin synthesis, which may explain why no general mechanism for lignification has yet been defined. The range of phenotypic effects observed include altered xylem sap transport, loss of mechanical support, reduced seed protection and dispersion, and/or increased pest and disease susceptibility.

From Zinnia to Arabidopsis: approaching the involvement of peroxidases in lignification

Zinnia elegans constitutes one of the most useful model systems for studying xylem differentiation, which simultaneously involves secondary cell wall synthesis, cell wall lignification, and programmed cell death. Likewise, the in vitro culture system of Z. elegans has been the best characterized as the differentiation of mesophyll cells into tracheary elements allows study of the biochemistry and physiology of xylogenesis free from the complexity that heterogeneous plant tissues impose. Moreover, Z. elegans has emerged as an excellent plant model to study the involvement of peroxidases in cell wall lignification. This is due to the simplicity and duality of the lignification pattern shown by the stems and hypocotyls, and to the basic nature of the peroxidase isoenzyme. This protein is expressed not only in hypocotyls and stems but also in mesophyll cells transdifferentiating into tracheary elements. Therefore, not only does this peroxidase fulfil all the catalytic requirements to be involved in lignification overcoming all restrictions imposed by the polymerization step, but also its expression is inherent in lignification. In fact, its basic nature is not exceptional since basic peroxidases are differentially expressed during lignification in other model systems, showing unusual and unique biochemical properties such as oxidation of syringyl moieties. This review focuses on the experiments which led to a better understanding of the lignification process in Zinnia, starting with the basic knowledge about the lignin pattern in this plant, how lignification takes place, and how a sole basic peroxidase with unusual catalytic properties is involved and regulated by hormones, H2O2, and nitric oxide.

Mechanisms for shaping, orienting, positioning and patterning plant secondary cell walls

Xylem vessels are cells that develop a specifically ornamented secondary cell wall to ensure their vascular function, conferring both structural strength and impermeability. Further plasticity is given to these vascular cells by a range of different patterns described by their secondary cell walls that-as for the growth of all plant organs-are developmentally regulated. Microtubules and their associated proteins, named MAPs, are essential to define the shape, the orientation, the position and the overall pattern of these secondary cell walls. Key actors in this process are the land-plant specific MAP70 proteins which not only allow the secondary cell wall to be positioned at the cell cortex but also determine the overall pattern described by xylem vessel secondary cell walls.