Isolation of the promoter region of <I>HAK</I> gene from <I>Aeluropus littoralis</I> and functional analysis in rice

Abstract

The AlHAK1 gene encoding a high-affinity K+ transporter was isolated from Aeluropus littoralis (Gouan) Parl, a graminaceous halophyte, and plays a crucial role in nutrition and ion homeostasis in plant cell. To investigate the regulation role of AlHAK1 on the transcriptional level, an about 1.3 kb 5'-flanking region of the AlHAK1 gene containing a putative promoter was cloned by genome walking method. Cis-regulatory elements analysis showed AlHAK1-promoter region contained typical TATA and CAAT boxes, and some growth and development relative motifs, as well as environmental re-sponsive elements. To reveal the function and regulating role, the AlHAK1 promoter was fused to the β-glucuronidase (GUS) reporter gene in the pCAMBIA1301 vector and introduced into rice via Agrobacterium-mediated transformation. Histo-chemical staining indicated that the GUS expression directed by AlHAK1 promoter was observed in leaves, stems, roots, anther, lemma, and palea. GUS quantitative fluorometric analysis indicated that GUS activity directed by AlHAK1 promoter was lower than CaMV35S and Ubiquitin constitutive promoters; however, in the roots and stems the GUS activity was rela-tively high and displayed a tissue-specific expression pattern. Under ABA, high temperature or drought stress, the GUS activity directed by AlHAK1 promoter was inducible in the roots and stems, suggesting the elements of HSE (-682 bp) and MybBS (-1 268 bp) might play a role in the inducible regulation.