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 - 1.34

DIFFERENTIAL EXPRESSED DNA FRACTION IN RIPENING STRAWBERRY (Fragaria vesca L.) FRUIT

SALUZZI D., SUNSERI F., GRECO I., MARTELLI G.

Dipartimento di Biologia, Difesa e Biotecnologie AgroForestali, Università degli Studi della Basilicata, Contrada Macchia Romana, 85100 Potenza

In the plants, the primary cell wall are described as several cellulose microfibrils embedded in a hemicellulosic polysaccharide matrix that interacts with an additional coextensive matrix of pectin and other less abundant components including structural proteins (Carpita & Gibeaut, 1993 - Plant J. 3: 1–30). In dicots the predominant hemicellulose is xyloglucan and it is thought that cellulose microfibrils are coated and tethered by a framework of xyloglucan polymers (Hayashi & Maclachlan, 1984 - Plant Physiol. 75: 596–604 McCann et al. 1990 - J. Cell Sci. 96: 323–334).

On the other hand, fruit ripening is a process that is regulated by multiple factors, including endogenous hormones. Auxin originating in the achenes regulates strawberry fruit development and maturation. Auxin is required for growth and early fruit development but acts to delay ripening (Given et al., 1988 - Planta 174: 402-406). Ripening of strawberry fruit is non-climacteric, occurring in the absence of ethylene. Several ripening-associated genes are expressed in strawberry fruit and the encoded proteins are potentially involved also in cell wall metabolism.

The expansins, a class of these proteins, are reported to be with no detectable enzymatic activity, but which induce increased extensibility in isolated plant cell walls in vitro (McQueen-Mason et al., 1995 -Plant Physiol. 107: 87–100). Expansins seem to be involved in the disruption of hydrogen bonds between cellulose and hemicellulose microfibrils in the cell wall (McQueen-Mason & Cosgrove, 1994 PNAS 91: 6574–6578). The expression of expansins in different growing organs (Cosgrove, 1997 – Ann. Rev. Cell Dev. Biol. 13: 171–201; Fleming et al., 1997 - Science 276: 1415–1418) would seem to confim their role in cell wall metabolism.

An expansin, LeExp1, was demonstrated to be expressed in ripening tomato fruit, a tissue characterized by extensive disassembly of cell wall polymers (Rose et al., 1997 - PNAS 94: 5955–5960). Also in strawberry (Fragaria x ananassa Duch.) an expansin gene, FaExp2, was detected during fruit ripening (Civello et al. 1999 – Plant Physiol. 121: 1273-79). In the present study, starting from four different genotypes of Fragaria vesca L. different strategies are proposed in order to isolate expansin gene, considering that FaExp2 is not closely related to LeExp1.

During ripening strawberry fruits from each genotypes of Fragaria vesca L. were harvested and classified for ripening stage as: small green, white, turning and ripe. The peduncle and calyx were removed, and the fruit were frozen in liquid nitrogen and stored at -80°C. Leaves tissues were collected, immediately frozen in liquid nitrogen, and stored at -80°C until use. Totally RNA and mRNA were isolated and cDNA was obtained in order to perform several experiments of differential display and cDNA-AFLP. Specific primers were also utilized in order to isolate sequences with high level of similarity with LeExp1 and FaExp2 genes.

The first experiments for differential expressed genes isolations showed, as expected, a low level of polymorphism either by differential display or by cDNA-AFLP. The first fragments differentially expressed among the ripening stages and coming from the different genotypes utilized will be sequence. The sequences obtained will compare against public databases for similarity with the expansin yet isolated.