Proceedings
of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress
Salsomaggiore Terme, Italy - 26/29 September, 2001
ISBN 88-900622-1-5
Oral Communication Abstract
ROLE OF THE ATHB-1 HD-ZIP TRANSCRIPTION FACTOR IN PLANT STRESS RESPONSES
LUCCHETTI S.*, BAIMA S.*, AOYAMA T.**, WISMAN
E.***, RUBERTI I.****, MORELLI G.*
* Istituto
Nazionale di Ricerca per gli Alimenti e la Nutrizione, Via Ardeatina 54,6,
00178 Roma
** Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
*** Michigan State University, East Lansing, Michigan 48824
**** Centro di studio per gli Acidi Nucleici, c/o Dipartimento di Genetica e Biologia Molecolare, Università di Roma La Sapienza, P. le Aldo Moro 5, 00185 Rome, Italy
ATHB-1, ethylene, HD-Zip transcription
factor, stress, target genes
The Arabidopsis ATHB-1 gene encodes a transcription factor of the
HD-Zip class. The expression analysis revealed that ATHB-1 mRNA is present in all plant
tissues, with the highest expression in the roots and flowers. Moreover, its
expression is regulated during plant growth. In particular we observed that the ATHB-1 expression increases in the leaf
with plant age reaching the highest level at bolting. This increase is
determined, in part, by ethylene as indicated by expression studies in ein2-1, etr1-1 and ctr1-1 ethylene mutants. Accordingly, the
gene is also rapidly induced by wounding, flooding and ethylene treatment. Previous
studies in transgenic tobacco overexpressing ATHB-1 have suggested that its function is concerned
with leaf development. This hypothesis has been recently supported by the
finding that cotyledon and leaf shape is altered in 35S:ATHB-1 Arabidopsis transgenic plants.
To gain more information on ATHB-1 function, a
search of athb1 insertional
mutants and of ATHB-1 putative target genes was undertaken. Six En1 insertions mapping close to the ATHB-1 gene were identified. One of them (athb1-1) located within the gene has been
further characterized. Northern analysis revealed that the ATHB-1 transcripts are below the level of
detection in athb1-1 plants. However, the phenotypic analysis of athb1-1 seedlings, performed under normal
growth conditions, showed no macroscopic developmental alterations. For
the search of ATHB-1 putative target genes, we constructed an ATHB-1-derived
transcription factor (HD-Zip-1-V-G) which is expected to recognize ATHB-1
target genes and transactivate them in a glucocorticoid-dependent fashion. In the presence of dexamethasone (DEX),
a glucocorticoid analogue, the HD-Zip-1-VG transgenic plants showed a phenotype
of narrow leaves with exagerated lobes, which was observed also as a severe
phenotype of 35S::ATHB-1 plants.
This result indicated that HD-Zip-1-V-G recognized the same target genes
as those of the authentic ATHB-1. The induction of the transactivating function
of HD-Zip-1-V-G does not require de novo protein synthesis, allowing us to
detect the target genes as up-regulated transcripts by DEX in the presence of
cycloheximide (CHX), an inhibitor of protein synthesis. We carried out a
target-gene analysis of ATHB-1 using this induction system in combination with
Arabidopsis genomic DNA clones and DNA microarrays. The analysis
identified so far genes involved in sugar metabolism and genes coding for amino
acid transporters. The expression analysis of these genes in wild-type and athb1-1 mutant plants, that should allow
the identification of ATHB-1 target genes, is currently in progress.
Biological meanings of
obtained candidates for target genes and the role of ATHB-1 in leaf development
and plant stress responses will be discussed.