BMC Genomics 2009, 10:415 http://www.biomedcentral.com/1471-2164/10/415 to be involved in hypo-osmotic turgor regulation [54]. Further, polyol transporter was shown to be expressed during maturation of common plantain companion cells [55], though its role in plant defense remains to be ambig- uous. These results suggest that transport of both organic and inorganic substances may play a crucial role in immune response. Genes involved in hormone responses Salicylic acid (SA), jasmonic acid (JA) and ethylene play key roles in developmental regulation and stress responses through cross communicating signal transduc- tion pathways. These hormones accumulate in response to pathogen infection and in turn lead to the activation of distinct sets of defense related genes [56]. We observed presence of ethylene signaling pathway genes, for exam- ple, ethylene responsive transcoactivator and putative eth- ylene response protein in the susceptible genotype while ethylene receptor was present only in the resistant geno- type. Coronatine-insensitive 1 and BRU1 precursor which are associated with JA and brassinosteroid pathways respectively, were specific to the resistant genotype. In addition, we found auxin signaling related proteins, of which, auxin-responsive SAUR was found in both the gen- otypes but auxin-regulated dual specificity cytosolic kinase was present only in the resistant genotype. Aux/IAA protein, auxin-induced protein IAA12 and auxin-induced putative aldo/keto reductase family protein were found specifically in the susceptible genotype. Our future efforts would be the investigation of their possible role in plant immunity. Genes involved in cell cycle and DNA metabolism Cell division and cell cycle progression in plants is often altered in response to various environmental stresses [57]. Many cell division and cell-cycle related proteins, for example, putative kinetochore, cell division protein FtsZ and cdc2MsF identified in this study were predominant in the resistant genotype suggesting pathostress responsive alterations of cell cycle in chickpea. Genes involved in DNA replication and repair like DNA repair protein RadA, putative polyprotein and putative gag-pol polyprotein were identified from susceptible genotype while putative helicase was common in both the genotypes. These find- ings are interesting because very little is known about the role of such genes in plant immune responses. Genes involved in development and cytoskeletal organization The genes involved in development and cytoskeletal organization account for 1.24% of the total CaUnigene set. The candidate genes involved in development were those encoding enzymes associated with fruit ripening and senescence, and several storage proteins like albumin and agglutinin. Most of the genes in this class were identi- fied in both the susceptible and resistant genotypes, how- ever agglutinin was specific to the resistant one. While there have been reports on association of the processes of plant defense and senescence [58], the involvement of rip- ening related proteins has never been implicated in immune responses. Seed storage proteins like germin and albumin have been shown to be involved in stress responses [59], however, role of agglutinin in plant immunity is not known. Cytoskeleton is thought to contribute to the establish- ment of effective barriers at the cell periphery against pathogen ingression. Substantiating this phenomenon, several structural proteins were identified that include actin, microtubule bundling polypeptide, and beta tubu- lin, besides genes associated with cytoskeletal reorganiza- tion like actin-depolymerizing factor and putative spindle disassembly related genes. Although actin was present in both the genotypes, actin-depolymerizing factor and putative spindle disassembly related genes were specific to resistant genotype. Genes involved in cellular redox and energy metabolism The oxidative burst is one of the earliest cellular responses following successful pathogen recognition. Several enzymes involved in oxidative burst were identified in both susceptible and resistant genotypes that include per- oxidase, superoxide dismutase, glutathione-S-transferase and quinone oxidoreductase. Apoplastic generation of superoxide or its dismutation product, hydrogen perox- ide, has been shown in response to a variety of pathogens [60]. These enzymes restrict the ROS-dependent damage and may lead to the activation of plant immune response [61]. Energy production has an impact on the overall metabolic state and the energy supply is the key factor for the main- tenance of cell intactness under various stress conditions. We observed the presence of genes encoding different pro- teins involved in ATP biosynthesis like alternative NAD(P)H dehydrogenase and putative ADP, ATP carrier- like protein in susceptible genotype. However, alternative oxidase 2b and NADH dehydrogenase were identified in the resistant genotype only. Nevertheless, vacuolar H+- ATPase subunit A and ATP synthase beta subunit were common to both genotypes. While the involvement of these proteins in abiotic stress, energy conservation and maintenance of redox potential is well established [62], their exact role in plant immune response is yet to be elu- cidated. Genes involved in secondary metabolism Most secondary metabolites of phenyl propanoid path- way, including lignins, isoflavonoid-phytoalexins and other phenolic compounds are instrumental in plant's Page 7 of 21 (page number not for citation purposes)