Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 5.17

LIGHT-INDUCED EXPRESSION OF A DEHYDRIN-ENCODING GENE OF SUNFLOWER

GIORDANI T., NATALI L., MAESTRINI P., MARTINELLI F., VERNIERI P., LERCARI B., CAVALLINI A.

Dipartimento di Biologia delle Piante Agrarie, Sezione di Genetica, Via Matteotti 1/B, 56124 Pisa

dehydrin, gene expression, light, promoter, sunflower

Dehydrins are an immunologically distinct family of proteins, produced by plants in the late stages of embryo development, but also following any environmental stimulus involving dehydration, such as drought or cold stress and salinity, as key components of dehydration tolerance. A dehydrin cDNA, HaDhn1, induced by drought stress, has been isolated and sequenced in sunflower, whose accumulation has been found to correlate to drought tolerance; this gene is expressed in the latest stages of Helianthus annuus embryogenesis, depending on abscisic acid accumulation; HaDhn1 transcripts accumulated after drought stress even in ABA-deficient sunflower mutants. Moreover, HaDhn1 is expressed also in plantlets exposed to low temperatures.

We have tested the effects of light quality on the expression of this gene. Plantlets of sunflower were germinated in the dark and, after 5 days, treated with different lights for 3, 6, 12, and 24 hours. Exposure to white light determined HaDhn1 transcript accumulation in the cotyledons, compared to plantlets grown in the dark. No differences in abscisic acid production were observed between light- and dark-grown plantlets. HaDhn1 transcripts increased also treating plantlets with monochromatic lights, either red and blue. However, red light induced higher transcripts levels than blue light, indicating phytochrome involvement in light signal transduction. Further experiments, performed saturating active phytochrome by yellow light, in combination or not with blue light, showed that also cryptochrome is involved in the HaDhn1 transcripts accumulation after exposure to light.

To verify possible mechanisms of induction of gene expression we have isolated and studied the putative promoter sequence of the HaDhn1 gene. Sequence analysis showed that different putative cis-elements recognizable by transcription factors occur in the isolated sequence: beside the putative TATA box (at -76 bp), one ABA-responsive element, one dehydration responsive element (DRE), two MYB- and one MYC- related elements were found. Moreover, a putative light-responsive G-box was found.

We are now performing Western blot analysis to verify if HaDhn1 RNA synthesis is followed by dehydrin-protein accumulation or not. If not, light-induced HaDhn1 gene expression might be considered as a preliminary response to possible drought stress conditions that can occur during the day in association to high light intensity.