Identification of drought-inducible regulatory factors in Lablab purpureus by a comparative genomic approach

Physiological indices of two lines of hyacinth bean (Lablab purpureus (L.) Sweet), MEIDOU 2012 and NANHUI 23, were compared during a progressive course of water-withholding treatments. MEIDOU 2012 was shown to be a superior drought-tolerant genotype. A suppressive subtractive hybridisation library was then constructed by using drought-stressed MEIDOU 2012 roots and sequenced to screen for transcripts with differential abundance variations. In total, 2792 unigenes were assembled from 4064 drought-induced expressed sequence tags. Comparative analysis with other legume genomic sequences, including soybean (Glycine max (L.) Merr.), common bean (Phaseolus vulgaris L.) and lucerne (Medicago sativa L.), was performed, from which 338 unigenes associated with root growth and drought response were identified. Among these unigenes, 27 transcription factors were deduced by functional-domain prediction. The transcription levels of a GRAS and a WRKY transcription factor were confirmed to be responding sensitively to water stresses. Additionally, protein–protein interaction (PPI) networks were predicted for all drought-induced root-related unigenes with different stringency levels. A mitogen-activated protein kinase (MAPK4) and an EF-hand calcium-binding protein (CML24) module were pinpointed to be putative ‘master’ signalling hubs in these PPI networks. Detailed examination of these genomic resources would further reveal key regulators of Lablab drought tolerance.