Cloning and Functional Analysis of an Aluminum Tolerance Candidate Gene GmSTOP1 in Soybean

Aluminum toxicity is one of the major factors that limits crop growth and production in acidic soils. AtSTOP1 transcription factor plays an important role in aluminum tolerance in Arabidopsis. To study the expression features and functions of the STOP1-like gene in soybean, we cloned a STOP1 gene located on chromosome 16 from the aluminum-toxicity tolerant soybean cultivar (Kefeng-1) using RT-PCR, and designated as GmSTOP1. Diverse cis-acting promoter elements involved in hormone and stress responses were discovered in the 1500 bp upstream region of GmSTOP1, such as ABRE, HSE and other elements. Protein structure prediction showed that GmSTOP1 contained four conservative Cys-2-His-2 zinc-finger domains. Phylogenetic analysis demonstrated that GmSTOP1 was similar to the putative STOP1-like protein from Phaseolus vulgaris. Subcellular localization showed that GmSTOP1 protein was located in the cell nucleus. The transcripts of GmSTOP1 were detected in all seven tissues tested including roots, shoot apical meristems, stems, leaves, flowers, pods and seeds. GmSTOP1 was up-regulated in soybean roots by 25 μM AlCl₃ treatment, and reached the highest relative expression level at 24 hours, which was about 9.2 times of the level in control (0 μM AlCl₃). Under 15 μM AlCl₃ (pH 4.3) treatment, the root lengths of two GmSTOP1 overexpressing transgenic Arabidopsis lines were significantly (P <0.05) greater than the wild type, as well as the relative root growth on AlCl₃ vs. pH 5.8 and pH 4.3 vs. pH 5.8. These results indicated that GmSTOP1 might participate in soybean response to aluminum-toxicity.