Agriculture Reference
In-Depth Information
required for establishment of vascular tissue, cytokinin signalling is necessary for
cell proliferation and the 'prepatterning' of four poles on which the vascular tissue
identity (consisting of the two xylem poles and two phloem poles) is established.
APL is necessary for this last phase of the vascular development.
8.5
Future prospects
Microarray technology provides a powerful tool for functional genomics and is being
widely used to shed light on global changes in gene expression. By clustering genes
according to their expression profile, it is possible to assign functions to genes with
an unknown function and at the same time to assign new functions to known genes.
Recently, a global gene expression map of the
Arabidopsis
root was made based on
microarray studies of various root cell types and tissues at progressive developmental
stages (Birnbaum
et al.
, 2003). The roots of plants expressing GFP in specific cell
types (in stele, endodermis, endodermis plus cortex, epidermal atrichoblast cells and
lateral root cap) were dissociated into single cells by enzymatic digestion of their cell
walls, the GFP-expressing cells were then isolated with the use of a fluorescence-
activated cell sorter and their mRNA was analysed with the use of microarrays.
Analysis of expression patterns revealed various clusters of genes with coordi-
nated expression in various spatial and temporal domains in root. For example, three
of these localized expression domains showed an aggregation of genes with known
or putative roles in auxin, gibberellic acid or jasmonic acid pathways, suggesting the
possibility of localized signalling centres which could mediate primary developmen-
tal cues (Birnbaum
et al.
, 2003). As described above, auxin is a major determinant
of patterning in root meristem. Increasing number of studies have shown that addi-
tional factors are required during root development and growth, among them also
other hormones. As increasing numbers of microarray experiments are completed,
the collections of data retrieved from different analyses will contribute to the reso-
lution of the complex relationships between the numerous signalling pathways that
underlie cell communication determining pattern formation and cell differentiation
during root development.
Acknowledgements
We thank Philip Benfey, Thomas Berleth, Gerd Jurgens, John C. Larkin, Ben Scheres
and John Schiefelbein for their permission to use their figures.
References
Aloni, R. (1987) Differentiation of vascular tissues.
Annu. Rev. Plant Physiol.
,
38
, 179-204.
Baker, D.A. (2000) Long-distance vascular transport of endogenous hormones in plants and their role in
source: sink regulation.
Isr. J. Plant Sci.
,
48
, 199-203.
