Identification of species-specific genes from Leucaena leucocephala using interspecies suppression subtractive hybridisation

Abstract

Leucaena leucocephala (leucaena) is a tropical tree-legume, known for its high level of tolerance to various stress conditions including drought and diseases. We hypothesised that leucaena contains a specific set of genes for tolerance to various abiotic and biotic stresses, which may be either absent or not expressed in other legumes that are susceptible to these stress conditions. Interspecies suppression subtractive hybridisation (iSSH) was used to identify some leucaena-specific genes using cDNAs from leucaena and Acacia confusa (acacia) as the tester and driver, respectively. Ninety-six leucaena genes showing homologies to various plant genes with known functions and 46 other genes encoding hypothetical proteins (hyps) were identified. Twenty-two genes encoded various stress-related proteins including chitinase, PR-10 protein, type 2 metallothionein, thaumatin-like protein, germin-like protein (GLP), molybdenum cofactor sulfurase (MCSU), aldehyde dehydrogenase, cysteine proteinase and Kunitz trypsin inhibitor. Conserved domain (CD) and position-specific iterative (PSI)-BLAST analyses predicted the possible functions of 15 hyps. The possible functions of the remaining hyps were predicted on the basis of various linear motifs. Six stress-related genes and 22 hyps were identified that expressed at higher levels under drought conditions in leucaena. The stress-related genes of leucaena identified through iSSH provide a foundation for future studies of molecular bases of stress tolerance in leucaena. These genes may also serve as a useful source of stress-tolerant genes for crop improvement in the future.