Isolation of MIP genes from olive (Olea europea L.)

Aquaporins are membrane-intrinsic proteins that belong to a highly conserved group of major intrinsic protein (MIP) family of channels. The aquaporins are distributed in animals, plants, fungi and bacteria. The function of these proteins is to facilitate the passive transport of water molecules down a water potential gradient. Olive (Olea europaea L.) is a typical Mediterranean tree which is adapted to arid climates. The molecular bases of water transport in olive have not been studied up to now, while in other fruit crops, such as the grapevine, aquaporin genes have been isolated and partially characterized. The aim of this work was to isolate MIPs from olive, and to characterize their physiological function. Roots, non-lignified shoot, leaves, and fruits were collected from olive plants cv. Leccino grown in a greenhouse. Total RNA was extracted from these tissues by a CTAB-based method. RT-PCR was used to isolate putative MIP sequences. The primers used were obtained from Arabidopsis PIP1;2 and tobacco NtAQP1 genes. Two different cDNA bands were obtained and sequenced, respectively of 580 and 600 bp, which showed a high (>80%) homology with known aquaporin genes. Based on homology analysis, the 580-bp sequence bears high similarity to PIP1 genes, while the 600-bp sequence is intermediate between PIP1 and PIP2 genes. Expression analysis was done on the two sequences, and revealed a different pattern of expression (with higher abundance respectively in leaves, and in roots). Isolation of the complete gene sequences is underway using RACE-PCR.