Functional Conservation and Divergence of Soybean GmSTOP1 Members in Proton and Aluminum Tolerance

Abstract

Proton (H⁺) and aluminum (Al) rhizotoxicity are two major factors limiting crop production in acid soils. Orthologs of the zinc-finger transcription factor, Sensitive To Proton Rhizotoxicity1 (STOP1), have been found to play an essential role in the tolerance to both stresses by regulating the transcription of multiple H⁺ and Al tolerant genes. In the present study, color three <i>GmSTOP1</i> homologs were identified in the soybean genome. All three <i>GmSTOP1</i> exhibited similar properties as reflected by the harboring of four potential zinc finger domains, localizing in the nucleus, and having transactivation activity. Expression profiling showed that H⁺ stress slightly modulated transcription of all three <i>GmSTOP1</i>s, while Al significantly up-regulated <i>GmSTOP1-1</i> and <i>GmSTOP1-3</i> in root apexes and <i>GmSTOP1-3</i> in basal root regions. Furthermore, complementation assays in an Arabidopsis <i>Atstop1</i> mutant line overexpressing these <i>GmSTOP1</i>s demonstrated that all three GmSTOP1s largely reverse the H⁺ sensitivity of the <i>Atstop1</i> mutant and restore the expression of genes involved in H⁺ tolerance. In contrast, only GmSTOP1-1 and GmSTOP1-3 could partially recover Al tolerance in the <i>Atstop1</i> mutant. These results suggest that the function of three GmSTOP1s is evolutionarily conserved in H⁺ tolerance, but not in Al tolerance.