Molecular Characterization of Type II Transposable Elements in Cowpea [Vigna unguiculata (L.) Walp]

Previous genetic studies in cowpea [Vigna unguiculata (L.) Walp] have shown that an active bipartite transposable element (TE) is responsible for a range of mutant phenotypes of its leaf, stem and flower. Since type II TEs have not been characterized at the molecular level in cowpea, this study was initiated to survey the presence of type II TEs in the cowpea genome. Type II TEs: Enhancer/Suppressor-mutator (En/Spm) and Miniature Inverted-repeat Transposable Elements (MITEs) were isolated and characterized. The sequence identity between the EnSpm TE clones was 46% at the nucleotide level (NL) and 30% at the amino acid level (AL) while that of MITEs was 71% at NL and 63% at AL. These cowpea En/Spm TEs were 80% homologous with En/Spm elements of other crops at NL and 46% at AL. The MITEs were 96% similar at NL and 18% homologous at AL. DNA gel blot analysis confirmed the presence of the En/Spm TEs in cowpea. RT-PCR (reverse transcriptase polymerase chain reaction) analysis showed that the VuEnSpm-3 and the MITE clone, VuPIF-1 were actively transcribed in wild type and mutant cowpea tissues. Overall, our data show that multiple, divergent lineages of En/Spm and MITEs are present in the cowpea genome, some of which are actively transcribed. Our findings also offer new molecular resource to further investigate the genetic determinants underlying previously described mutant cowpea phenotypes.