Abstract
Aluminum (Al) toxicity is the primary limiting factor that affects crop yields in acid soil. However, the genes that contribute to the Al tolerance process in maize are still poorly understood. Previous studies have predicted that ZmAT6 is a novel protein which could be upregulated under Al stress condition. Here, we found that ZmAT6 is expressed in many tissues and organs and can be dramatically induced by Al in both the roots and shoots but particularly in the shoots. The overexpression of ZmAT6 in maize and Arabidopsis plants increased their root growth and reduced the accumulation of Al, suggesting the contribution of ZmAT6 to Al tolerance. Moreover, the ZmAT6 transgenic maize plants had lower contents of malondialdehyde and reactive oxygen species (ROS), but much higher proline content and even lower Evans blue absorption in the roots compared with the wild type. Furthermore, the activity of several enzymes of the antioxidant system, such as peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), increased in ZmAT6 transgenic maize plants, particularly SOD. Consistently, the expression of ZmSOD in transgenic maize was predominant upregulated by Al stress. Taken together, these findings revealed that ZmAT6 could at least partially confer enhanced tolerance to Al toxicity by scavenging ROS in maize.
Highlights
Acidic soils refer to soil with pH ≤ 5.5, occupying almost 30% of the arable soil and 50% of the potential cultivated land (von Uexküll and Mutert, 1995)
No distinct difference could be detected between the OE-ZmAT6 lines and wild type (WT) regarding these two indices. Both H2O2 and the superoxide anion had increased in all the plants tested during Al stress, and the amplitude was even higher in the WT than in OE-ZmAT6 plants (Figures 6A, B).The increase of H2O2 content and productive rate of superoxide anion in WT against OEZmAT6 lines under Al stress were 0.38:0.09 and 0.24:0.11 min, respectively. These results indicated that ZmAT6 played an important role in the scavenging of the excessive reactive oxygen species (ROS) caused by Al stress, which endowed transgenic maize plants with the capacity to tolerate aluminum toxicity by ROS cleaning
ZmAT6 was first identified as an Al-induced gene with an unpredicted function from our previous microarray data (Xu et al, 2017)
Summary
Acidic soils refer to soil with pH ≤ 5.5, occupying almost 30% of the arable soil and 50% of the potential cultivated land (von Uexküll and Mutert, 1995). The internal tolerance mechanism refers to the sequestration of Al into vacuoles and its detoxification by chelation (Ma, 2000; Zheng and Yang, 2005). Both mechanisms are controlled by the expression of a series of genes. Many genes related to Al tolerance have been identified, such as organic acid transporter genes (ALMTs and MATEs) (Hoekenga et al, 2006; Furukawa et al, 2007; Liu et al, 2013), antioxidative stress-related genes (Wu et al, 2017), including those encoding aluminum transporter (Nramps and ABC transporter, aquaporins) (Huang et al, 2012; Li et al, 2014; Kochian et al, 2015; Lu et al, 2017; Wang et al, 2017), enzymes related to cell wall polysaccharide metabolism (XTHs) (Zhu et al, 2012; Zhu et al, 2014), and transcription factor (STOP, WRKY, ASR, NAC) (Iuchi et al, 2007; Ding et al, 2013; Arenhart et al, 2016; Li et al, 2018; Lou et al, 2019)
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