Molecular identification and chromosomal localization of genes encoding Triticum aestivum xylanase inhibitor I-like proteins in cereals.
TAXI ( Triticum aestivum xylanase inhibitor) proteins are present in wheat flour and are known to inhibit glycosyl hydrolase family 11 endoxylanases, enzymes which are commonly applied in grain processing. Here, we describe the PCR-based molecular identification of genes encoding endoxylanase inhibitors HVXI and SCXI, the TAXI-like proteins from barley ( Hordeum vulgare) and rye ( Secale cereale) respectively. The HVXI coding sequence encodes a mature protein of 384 amino acids preceded by a 19 amino acid long signal sequence. SCXI-II/III has an open reading frame encoding a signal peptide of 21 amino acids and a mature protein of 375 amino acids. As for TAXI-I, no introns were detected in the untranslated regions and coding sequences identified. These newly identified sequences allowed us to perform a multiple sequence alignment with TAXI-I and similar proteins. Rice TAXI-type proteins clustered together with the cereal endoxylanase inhibitors. Dicotyledonous proteins with sequence similarity to TAXI-I, including the tomato xyloglucan-specific endoglucanase inhibiting protein, formed a different clade. The TAXI-type proteins may hence be part of a superfamily of proteins all involved in plant responses to biotic or abiotic stress and for which a function as glycosyl hydrolase inhibitors can be suggested. The chromosomal localization of the TAXI-I gene identified on wheat chromosome 3B, of the SCXI-II/III gene identified on rye chromosome 6R, and the presence of a cluster of TAXI-like genes on rice chromosome 1, allowed us to assign the location of TAXI-like genes to the wheat-rye translocation area 3BL/6RL characterized by RFLP markers XGlb33 and Xpsr454 and isozyme Est-5. In rice, RFLP marker C1310S corresponds to a TAXI-like protein encoding sequence.