INTRODUCTION The main feature that distinguishes the avocado fruit Persea americana Mill. is the high content of oil in the mesocarp, which gives the fruit its creamy texture and contributes to its flavor. The oil is a source of saturated palmitic and stearic acid , monounsaturated oleic and palmitoleic acid , and polyunsaturated linoleic and linolenic acid fatty acids that impart health benefits through anticholesterolemic, antioxidant, and anti-inflammatory activities 1 3. Studies on avocado fruit oil have mostly focused on the commercial cultivars, such as Hass, Bacon, and Fuerte, whereas few studies have been carried out on the fruits of native Mexican P. americana var. drymifolia and American P. americana var. americana varieties, despite their excellent medicinal and nutritional properties 4 7. The avocado tree belongs to the family Lauraceae, a primitive group of Angiosperms that was domesticated during the pre-Hispanic period in Mesoamerica as three botanical varieties P. americana var. americana, P. americana var. guatemalensis, and P. americana var. drymifo

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Avocado native "Mexicano" (Persea americana var drymifolia) has been a really important species in agricultural and indigenous medicine. In the agricultural world, it has been the germplasm source for the generation of economically important cultivars like Hass and it is the main source of rootstocks for the world production of Hass avocado fruit. In spite of its importance, little is known about the molecular network of seed-fruit development. The aim of this work was to know the expressed genes (ESTs) during the early avocado native "Mexicano" seed development. Using total RNA we constructed cDNA libraries of fourth months seed development, sequencing, assembling and bioinformatic analysis was made. For validation, a semi-quantitative PCR experiments with the most abundant genes were made. About 5005 ESTs from the 5' representing 1653 possible unigenes were isolated. After assembling process, we have 171 genes that are closely related to Nelumbo nucifera sequences. The transcriptome is dominating by one bHLH transcription factor, three metallothioneins and snakin, suggesting its main role in seed development. Until now, there are no molecular studies in avocado seed development.