Biotecnologia Aplicada Elfos Scientiae ISSN: 0684-4551 Vol. 13, Num. 2, 1996

Analysis of promoters active in specific cell types in the radicular system of Zea mays

Montserrat Capellades, Miguel Angel Torres, Xavier Uribe, Florence Vignols, Joan Rigau and Pere Puigdomenech

Molecular Genetic Department. CID-CSIC. Jordi Girona, 18. 08034 Barcelona. Spain.

Code Number: BA96053
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The expression of two families of genes in the root system has been analized in maize. Those correspond to genes coding for alfa-tubulin and for caffeic acid o-methyltransferase, an enzyme of the lignin biosynthesis pathway. In maize seven or eight genes code for alfa-tubulin (1). Three of these genes have been cloned in our Department. Two of these genes, genes tubalfa1 and tubalfa2, are forming a tandem in the genome of maize separated by 1 kb approximately (2). The other gene tubalfa3 is located in a different chromosomal localization (3). The analysis of mRNA accumulation of the three characterized alfa-tubulin genes indicates that they are mostly expressed in the meristematic regions of the plant. However it was found that gene tubalfa1 has a preferential expression in the radicular system and in the pollen, while for tubalfa3 this preference is not observed.

Studies using in situ hybridization indicate that the three genes are active in different cell types. In the root meristem gene tubalfa2 is expressed in the subepidermal layers of the root meristem, tubalfa1 mRNA is accumulated in dividing cells produced from the quiescent centre and in the cells precursor of cortex and endodermis while tubalfa3 mRNA is concentrated to a higher extent in the pericycle and the steele. The genes coding for tubulins alfa1, alfa2 and alfa3 have been sequenced and the promoter region has been fused to the to the beta-glucuronidase reporter gene. The three promoters are active in tobacco transgenic plants as it has been described for gene alfa promoter (4).

Most of the features already observed in maize for the mRNA accumulation of these genes are conserved in the transgenic plants allowing to dissect the promoter. The promoters can be useful when a specific function may be directed to specific cell types in root meristem.

The other family of genes studied is the one coding for caffeic acid O-methyltransferase (OMT). This is one of the enzymes of the pathway producing lignin monomers.

The gene has been cloned in maize (5) and it is a single gene whose mutation produces a reduction in lignin and a characteristic phenotype known as brown-midrib3 in classical maize genetics (6). The mRNA accumulation is observed in maize in very precise location in the root and shoot with an excellent correlation with cells undergoing lignification. In particular, a high mRNA accumulation is observed in the leaf midrib. The promoter of the gene is active in both maize and tobacco transgenic plants and it appears as an excellent promoter when modulation of lignin content by molecular means is the goal of the work.

1. Montoliu L, Rigau J and Puigdomenech P. Analysis by PCR of the number of homologous genomic sequences to alfa-tubulin in maize. Plant Sci 1992;84:179-185.

2. Montoliu L, Rigau J and Puigdomenech P. A tamdem of alfa- tubulin genes preferentially expressed in the radicular system of Zea mays. Plant Mol. Biol 1989;14:1-15.

3. Montoliu L, Puigdomenech P. and Rigau J. The tubalfa3 gene from Zea mays: structure and expression in dividing plant tissues. Gene 1990;94:201-207.

4. Rigau J, Capellades M, Montoliu L, Torres MA, Romera C, Mart¡nez-Izquierdo JA, Tagu D. and Puigdomenech P. Analysis of the maize alfa-tubulin gene promoter by transiet expression and in transgenic tobacco plants. Plant J 1993;4:1043-1050.

5. Collazo P, Montoliu L, Rigau J and Puigdomenech P. Structure and expression of the lignin o-methyltransferase gene in Zea mays. Plant Mol. Biol 1992;20:857-867.

Copyright 1996 Elfos Scientiae