Soybean is an important crop for oil and protein resources but its growth and development may encounter various abiotic stresses, including high salinity, that can hinder soybean production. Manipulation of soybean stress tolerance requires a thorough understanding of the mechanisms underlying plant response to stresses. Evolutionarily, plants have developed multiple gene regulatory mechanisms to adjust cellular activities for better survival under stress conditions, and one of these is microRNA (miRNA)-mediated gene silencing (Zhang, 2015). Many conserved and novel miRNAs have been identified in different organs of soybean and in different processes during soybean development (Song et al., 2011). However, these soybean miRNAs were seldom studied in stress response. Previously, we have identified multiple stressresponsive transcription factor genes from soybean and analyzed their functions in stress response (Wei et al., 2009; Wang et al., 2015). Now we intend to explore the role of miRNAs in the regulation of soybean response to stresses. Among our previously identified miRNAs from soybean (Song et al., 2011), the gma-miR172a can be induced by salt and other stresses, and so was selected for further investigation.

Alfin-like (AL) is a small plant-specific gene family with prominent roles in root growth and abiotic stress response. Here, we aimed to identify novel stress tolerance AL genes from the stress-tolerant species Atriplex hortensis. Totally, we isolated four AhAL genes, all encoding nuclear-localized proteins with cis-element-binding and transrepression activities. Constitutive expression of AhAL1 in Arabidopsis facilitated plants to survive under saline condition, while expressing anyone of the other three AhAL genes led to salt-hypersensitive response, indicating functional divergence of AhAL family. AhAL1 also conferred enhanced drought tolerance, as judged from enhanced survival, improved growth, decreased malonaldehyde (MDA) content and reduced water loss in AhAL1-expressing plants compared to WT. In addition, abscisic acid (ABA)-mediated stomatal closure and inhibition of seed germination and primary root elongation were enhanced in AhAL1-transgenic plants. Further analysis demonstrated that AhAL1 could bind to promoter regions of GRF7, DREB1C and several group-A PP2C genes and repress their expression. Correspondingly, the expression levels of positive stress regulator genes DREB1A, DREB2A and three ABFs were all increased in AhAL1-expressing plants. Based on these results, AhAL1 was identified as a novel candidate gene for improving abiotic stress tolerance of crop plants.