A Comparative Study of ESTs Induced under Drought and Salinity Stress in Hyacinth Bean (Lablab purpureus)

Abiotic stressors like drought and salinity are major causes for loss of agricultural productivity. Comparison of expressed sesquence tags (ESTs) under different abiotic stresses provides insight into underlying mechanism of stress response, and candidate genes to improve tolerance to abiotic and biotic stresses via breading and transgenic methods. In order to identify and compare stress-specific ESTs from drought and salinity stressed Hyacinth Bean, ten days old seedlings were subjected to respective stresses and RNA was extracted from control and stressed leaves for EST identification. 31 and 12 ESTs, respectively, were characterized from leaves of drought and salinity stressed seedlings of Hyacinth Bean, Lablab purpureus by differential display RT-PCR using identical combinations of 48 primers and validated using quantitative RT-PCR. Relative fold expression was higher under salt stress than drought stress. Whereas 19 EST overexpressed under drought, 12 EST were down regulated. Of the 12 EST under salinity, 9 EST were downregulated and 3 EST upregulated. Putative functions predicted from sequence homology indicated that 11 drought specific EST corresponded to metabolic functions, and 4 of them corresponded to transcription regulation. Under salinity, 4 and 2 EST, respectively, corresponded to metabolic and RNA associated functions. Under both stresses, there were ESTs associated with unknown functions, whose characterization may throw light on the regulatory mechanism. Differing number of ESTs differentially expressed under drought and salt stress, and their predicted functionalities, suggested distinct set of response genes involved under these two stresses, despite a good number of physiological players being common. From the predicted functions of ESTs, the paper attempts to explain the possible mechanism of response of Hyacinth Bean to these two stresses.