Repertoire of leaf expressed sequence tags (ESTs) and partial characterization of stress-related and membrane transporter genes from mulberry (Morus indica L.)

The foliage of mulberry, Morus indica, serves as feed for the silkworm, and developing elite cultivars of this species is thus vital for the sericulture industry. However, due to lack of information on the molecular control of its cellular metabolism, it is difficult to design strategies for genetic engineering for improvement of this species of immense economic importance. We report here the construction of a complementary DNA (cDNA) library from mature leaf of mulberry based on Universal PCR amplification method. The library is enriched in transcripts ranging from 1 to 2 kb. In this study, a total of 1,500 randomly selected clones were isolated and sequenced from the leaf cDNA library of M. indica var. K2. Based on sequence homology with available databases, expressed sequence tags (ESTs) were further assigned into functional categories with protein metabolism (15%), transport (8%), stress-related proteins (9%), energy (5%), and photosynthesis (4%). A large group amongst the total ESTs (22%) did not show any significant homology with known proteins. Several abiotic stress-related clones, including membrane transport proteins like vacuolar Na+/H+ antiporter, aquaporins, and stress-related proteins like LEA, RD22, dehydrins, and HAL3, were obtained in this library. Some of the selected clones have been characterized further by studying their transcript levels in different tissues as well as under various abiotic stress conditions. The identification of a large number of genes encoding enzymes involved in various secondary metabolites in mulberry opens up new avenues for research on natural product chemistry in mulberry.