The inventors herein disclose a new transporter that participates in guard cell movement. The inventors have now found that AtCHX20 is preferentially expressed in guard cells using microarray and promoter TGUS analyses. The inventors have also found a guard cell specific promoter which serves as a powerful tool to manipulate the opening and closing of guard cells and thus the ability to control water loss and gas exchange of plants. Such a tool can be particularly useful when applied to crops and other plants of economic importance, thus the present inventors have identified homologous genes in several other plants that fall within the scope of this invention.