Down-regulation of ZmEXPB6 (Zea mays β-expansin 6) protein is correlated with salt-mediated growth reduction in the leaves of Z. mays L.

The salt-sensitive crop Zea mays L. shows a rapid leaf growth reduction upon NaCl stress. There is increasing evidence that salinity impairs the ability of the cell walls to expand, ultimately inhibiting growth. Wall-loosening is a prerequisite for cell wall expansion, a process that is under the control of cell wall-located expansin proteins. In this study the abundance of those proteins was analyzed against salt stress using gel-based two-dimensional proteomics and two-dimensional Western blotting. Results show that ZmEXPB6 (Z. mays β-expansin 6) protein is lacking in growth-inhibited leaves of salt-stressed maize. Of note, the exogenous application of heterologously expressed and metal-chelate-affinity chromatography-purified ZmEXPB6 on growth-reduced leaves that lack native ZmEXPB6 under NaCl stress partially restored leaf growth. In vitro assays on frozen-thawed leaf sections revealed that recombinant ZmEXPB6 acts on the capacity of the walls to extend. Our results identify expansins as a factor that partially restores leaf growth of maize in saline environments.