15th International Conference on Arabidopsis Research - TAIR

T02-025
ROOT HAIR PATTERNING AND THE REGULATION OF
ROOT HAIR-SPECIFIC GENES
Hyung-Taeg Cho(1), Sang Ho Lee(1), Dong Wook Kim(1)
1-School of Biosciences and Biotechnology, Chungnam National University, Daejoen 305-764,
Korea
Arabidopsis expansin (the cell wall-loosening factor) 7 gene (AtEXP7) expresses
specifically in the root epidermal cells from which root hairs differentiate,
resulting in a striped expression pattern along the root hair-forming cell files.
The gene expression is closely correlated with root hair initiation, suggesting
that expansin-mediated wall loosening is required for hair emergence from
the epidermal cell. Promoter analyses showed the essential cis-element
for this root hair-specificity and also for the responsiveness to hormones
and environmental factors of the gene expression. A putative transcription
factor capable of binding this element was identified by yeast one-hybrid
screening. Three different types of root hair cell arrangement are recognized
in vascular plants, where different cell fate machineries should direct the
distinct patterns. Intriguing questions on this matter are '(1) Do the different
hair-patterning species have orthologs of AtEXP7? (2) Are the AtEXP7
orthologous genes expressed in the same manner as in Arabidopsis? This
casts a fundamental question on the evolution of cell differentiation: 'Does
patterning unilaterally dictate cell differentiation?' or 'Does cell differentiation
hire patterning as to serve in a special multicellularity situation?' We present
some preliminary results to answer these questions. (This research was supported
by the grants from Plant Diversity Research Center, 21C Frontier R&D
Programs and from Environmental Biotechnology Research Center.)
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T02-026
The AtMYB11 gene is a possible regulator of
development in Arabidopsis thaliana
K. Petroni(1), V. Calvenzani(1), D. Allegra(1), G. Falasca(2), MM. Altamura(2), C.
Tonelli(1)
1-Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via
Celoria 26, 20133 Milano, Italy
2-Dipartimento di Biologia Vegetale, Università “La Sapienza”, Piazzale Aldo Moro 5, 00185 Roma,
Italy
MYB proteins are transcription factors sharing a characteristic DNA-binding
domain shown to bind DNA in a sequence specific manner. MYB proteins
in animals contain three repeats (R1, R2, R3), while in plants this domain
generally consists of two imperfect repeats of about 50 residues (R2, R3). In
Arabidopsis, more than 125 R2R3-MYB genes have been identified, representing
one of the widest family of plant transcription factors described. The
information available on the function of a few plant MYB proteins suggest an
important role of this family in various processes like regulation of metabolic
pathways, control of cell division and plant morphogenesis, response to
different stresses and involvement in hormone signal transduction.
RT-PCR analyses showed that one of the genes under study in our laboratory,
AtMYB11, was expressed throughout flower development and in 4 days-old
seedlings, where the activation is mediated by light. Subsequent analyses
by in situ hybridization and promoter-GUS fusions revealed that AtMYB11 is
specifically expressed in meristems and primordia of Arabidopsis. In fact, the
AtMYB11 transcript is found mainly in the shoot and root apical meristems
of seedlings, but also in young cotyledons and secondary root primordia. In
addition, AtMYB11 is expressed in the inflorescence meristems, in axillary
meristems of stem and in flower primordia. During flower development the
transcript is present in ovule primordia, in the ovary wall of mature ovules
and in the embryo epidermis of developing seeds.
Two dSpm insertion mutants has been isolated from the Wageningen collection
and for one of them homozygous knock-out plants has been analysed
in all growth phases. These mutants are morphologically similar to wild-type
plants, however they show an accelerated germination and morphogenesis.
In particular, they show an earlier development of seedling organs and an
accelerated emergence and differentiation of leaves, inflorescences and
roots. This acceleration leads to early flowering plants with more lateral
inflorescences, flowers and more adventitious and lateral roots. Furthermore,
flowers produce shorter siliques and less seeds than wild-type.
Since three additional dSpm insertions are present in the background of the
mutant plants analysed, a second independent insertion mutant, but also
RNAi and overexpression plants are currently under analysis, in order to confirm
that the accelerated growth depends on the mutation in the AtMYB11
gene.
T02 Development 2 (Shoot, Root)