GENETICS AND GENOMICS Characterization and expression of plasma and tonoplast membrane aquaporins in elongating cotton fibers Diqiu Liu Æ Lili Tu Æ Li Wang Æ Yunjing Li Æ Longfu Zhu Æ Xianlong Zhang Received: 27 January 2008 / Revised: 18 March 2008 / Accepted: 25 March 2008 / Published online: 5 April 2008 Ó Springer-Verlag 2008 Abstract Cotton fiber (Gossypium hirsutum L. and G. barbadense L.) is a good model for studies of plant cell elongation and cell wall biogenesis. Aquaporins are ancient membrane channel proteins that facilitate the permeation of water across biological membranes. We studied GhPIP1-2, encoding plasma membrane intrinsic protein, and GhcTIP1, encoding tonoplast intrinsic protein, during cotton fiber development. The full-length cDNAs of GhPIP1-2 and GhcTIP1 were obtained through 5 0 RACE. The deduced amino acid sequences of GhPIP1-2 and GhcTIP1 share high sequence identity with aquaporins from diverse plant spe- cies. Phylogenetic analysis of GhPIP1-2 and GhcTIP1 with other plant aquaporins showed that GhPIP1-2 belongs to the PIP1 group of the PIP subfamily and GhcTIP1 belongs to the cTIP group of the TIP subfamily. GhPIP1-2 and GhcTIP1 contain three and two introns, respectively. Genomic Southern blot analysis indicated that GhPIP1-2 and GhcTIP1 have several copies and multiple homologous genes in allotetraploid cotton. Northern blot analysis with gene-specific probes and real-time PCR demonstrated that GhPIP1-2 and GhcTIP1 are predominantly expressed dur- ing cotton fiber elongation, with the highest expression levels at 5 days post-anthesis. Moreover, expression pat- terns of the two genes in G. hirsutum and G. barbadense are similar, whereas the expression levels in G. barbadense are much lower than that in G. hirsutum. The high and prefer- ential expression of GhPIP1-2 and GhcTIP1 during fiber cell elongation suggests that they may play important roles in supporting the rapid influx of water into vacuoles during cotton fiber cell expansion. Keywords Aquaporin Á Cotton fiber development Á Gossypium Á Plasma membrane intrinsic protein Á Tonoplast intrinsic protein Abbreviations AQP Aquaporin DPA Days post anthesis ESTs Expressed sequence tags NIP Nodulin26-like intrinsic protein ORF Open reading frame PIP Plasma membrane intrinsic protein QRT-PCR Quantitative reverse transcription-PCR RACE Rapid amplification of cDNA ends SIP Small basic intrinsic protein TM-1 Texas Marker-1 TIP Tonoplast intrinsic protein Introduction The two cultivated species of cotton, G. hirsutum and G. barbadense, have an important status in international economies because cotton is the major natural fiber used in textiles. Besides the economic importance of the fiber, developing cotton fiber provides a unique experimental system to study cell differentiation, cell elongation, and cell wall biosynthesis. Cotton fibers are seed trichomes that result from elongation of epidermal cells of the ovule and have several distinguishing features. First, cotton fiber is unicellular, and its development does not include the Communicated by K. Toriyama. D. Liu Á L. Tu Á L. Wang Á Y. Li Á L. Zhu Á X. Zhang (&) National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, Hubei 430070, China e-mail: xlzhang@mail.hzau.edu.cn 123 Plant Cell Rep (2008) 27:1385–1394 DOI 10.1007/s00299-008-0545-6