Aluminum (Al) toxicity is a global agricultural problem that severely limits root growth and crop productivity in regions with acidic soils, which represent upwards of 50% of the world's arable land. Significant progress has been made toward understanding how plants cope with Al in their environment, yet our knowledge of how Al toxicity leads to root growth inhibition is lacking. Using a genetic approach with the plant model system Arabidopsis, it has been determined that Al-dependent root growth inhibition is largely an active process that occurs in response to detection of DNA damage. Mutational loss of factors required for detection of this damage actually leads to increased root growth, which suggests that Al functions as a mild agent of DNA damage in vivo. Further work is aimed at determining the nature of the Al-dependent DNA damage, which is speculated to lead to heritable changes since Al is capable of causing DNA crosslinks in vivo. Techniques to be used include monitoring DNA integrity over several generations following exposure to Al along with identification and analysis of additional biochemical components that are required for detection and response to Al toxicity. Through these analyses, it will be possible to gain a better understanding of how Al causes root growth inhibition while at the same time determine the in vivo effect of Al on DNA integrity, the latter of which has been intensively debated with regard to impacts on both plants and animals. Through this work, the PI will be able to continue an ongoing commitment to promotion of creativity in the local school district along with providing intensive mentoring opportunities in a laboratory environment to students from underrepresented groups.

Project Report

Aluminum is the third most abundant element and most abundant metal in the earth’s crust, yet unlike other metals it has no biochemical role in biological systems. Instead, internalization of aluminum in plant tissue leads to severe inhibition of root and shoot growth. This is particularly a problem in many developing countries in Africa and South America that have extensive acid soil regions, which is the environment in which the phytotoxic form of aluminum predominates. Consequently, development of an understanding of how aluminum stops root growth is essential for improving global agricultural productivity. It has previously been speculated that the mechanism(s) by which aluminum stops root growth is a highly complex phenomenon due to the likely non-specific nature of binding of aluminum to biological targets. In contrast, it has been found recently that aluminum dependent root growth inhibition is largely an active process that is mediated by components that regulate the DNA damage checkpoint, including Ataxia telangiectasia and Rad3 related protein (ATR), which is a key factor universally found in higher eukaryotes that is responsible for monitoring for stresses that effect DNA replication and promote persistent single-stranded DNA. As a continuation of this work, other biochemical factors that function with ATR to monitor aluminum-dependent effects on genome integrity have been found. These factors include the WD-40 protein, ALT2, and the p53-like transcription factor, SOG1, which have been found to function in conjunction with ATR to promote expression of Al responsive genes. This transcriptional program is thought to be responsible for stoppage of cell cycle progression, inhibition of root growth, and terminal differentiation of the root tip in conjunction with loss of the quiescent center. Loss-of-function mutants for any of these factors results in failure to initiate these programmed responses and leads to roots that are capable of maintaining root growth even in the presence of normally severely inhibitory levels of aluminum. Consequently, it appears that stoppage of root growth following aluminum treatment is largely an active process that results from ATR, ALT2, and SOG1 perceiving aluminum as being a genotoxic agent. This indicates that modification of this DNA damage response pathway may be an effective strategy for conferring aluminum tolerance in agriculturally relevant crops to allow for growth in aluminum toxic acid soils.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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Sarah Wyatt
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University of California Riverside
United States
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