ORIGINAL ARTICLE Induction of salt tolerance and up-regulation of aquaporin genes in tropical corn by rhizobacterium Pantoea agglomerans S.K. Gond 1,2 , M.S. Torres 1 , M.S. Bergen 1 , Z. Helsel 1 and J.F. White Jr 1 1 Department of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ, USA 2 Department of Botany, Visva-Bharati, Santiniketan, WB, India Significance and Impact of the Study: The enhancement of salt tolerance capacity in tropical corn, an important food crop, has the capacity to increase its cultivation area and yield in saline soils. The appli- cation of rhizobacteria to improve salt tolerance of tropical corn is ecofriendly and cost effective. We show that P. agglomerans isolated from teosinte (an ancestor of corn) induces salt tolerance in tropical corn and up-regulation of aquaporin genes. This study shows that microbes that increase salt tolerance may be used to enhance crop growth in saline soils. Keywords aquaporin, endophyte, maize, rhizobacterium, salt stress. Correspondence Surendra K. Gond, Department of Botany, Visva-Bharati, Santiniketan, WB, India. E-mail: surendragond@gmail.com and James F. White Jr, Department of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ, USA. E-mail: jwhite3728@gmail.com 2014/2001: received 26 September 2014, revised 20 December 2014 and accepted 23 December 2014 doi:10.1111/lam.12385 Abstract Bacteria were isolated from surface disinfected seeds of eight modern corn types and an ancestor of corn, ‘teosinte’ and identified using 16S rDNA sequences. From each of the modern corn types we obtained Bacillus spp. (including, Bacillus amyloliquefaciens and Bacillus subtilis); while from teosinte we obtained only Pantoea agglomerans and Agrobacterium species. Of these bacteria, only P. agglomerans could actively grow under hypersaline conditions and increase salt tolerance of tropical corn seedlings. In laboratory and greenhouse experiments where plants were watered with a 0Á2 mol l À1 NaCl solution, P. agglomerans was found to enhance the capacity of tropical corn to grow compared to uninoculated controls. The total dry biomass was significantly higher in P. agglomerans-treated plants compared to controls under saline water. Gene expression analysis showed the up-regulation of the aquaporin gene family especially plasma membrane integral protein (ZmPIP) genes in P. agglomerans-treated plants. The plasma membrane integral protein type 2 (PIP2-1) gene in tropical corn seedlings was highly up-regulated by P. agglomerans treatment under salt stress conditions. Microscopic examination of P. agglomerans inoculated seedlings revealed that the bacterium colonized root meristems densely, and as roots developed, the bacterium became sparsely located in cell junctions. Introduction In the process of growth and development, plants encounter both biotic (e.g., pests and pathogens) and abi- otic environmental stresses (e.g., drought, heavy metals, heat and salt). There are pesticides available to control pests and pathogens but it is often difficult to control environmental stresses. Abiotic environmental stresses, like soil salinity and drought are common crop yield lim- iting factors. About 2Á5% of the earth’s water is fresh or with low salt concentration (<1 dS m À1 ) and can be used for crop irrigation; the rest of water is saline and cannot be used for crop production (Ondrasek et al. 2010). Extensive irrigation with saline water and application of fertilizers create soils unsuitable for crop production (McKersie and Leshem 1994). Salinity is one of the most important environmental stresses which affect the produc- tivity of agricultural crops, with adverse effects on germi- nation, plant vigour and crop yield (Munns and Tester 2008). More than 45 million hectares of land worldwide Letters in Applied Microbiology 60, 392--399 © 2015 The Society for Applied Microbiology 392 Letters in Applied Microbiology ISSN 0266-8254