Submitted to: New Phytologist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/8/2008
Publication Date: 7/1/2008
Citation: Maron, L.G., Matias, K., Mao, C., Menossi, M., Kochian, L.V. 2008. Transcriptional profiling of Al toxicity and tolerance responses in maize roots. New Phytologist. 179:116-128. Interpretive Summary: Large areas of land within the U.S. and over 40% of the world’s lands are acidic, where aluminum (Al) toxicity is the primary factor limiting crop production via inhibition of root growth. The physiological and molecular basis for Al tolerance is still poorly understood. Thus, we need a more complete understanding of the mechanisms and associated genes underlying Al tolerance if we are going to be able to develop more Al tolerant crop plants for improved cultivation on acid soils. In this paper, we used maize gene chip technology to simultaneously quantify the level of expression of thousands of genes in the maize root tip of an Al tolerant compared with an Al sensitive line of maize, during the onset (first 24 hours) of Al stress. This approach was employed to identify candidate Al tolerance genes based on the hypothesis that Al tolerance genes may be more highly expressed constitutively or upon Al exposure in the root tip (the site of Al toxicity)of tolerant maize lines. Using this approach, we identified several candidate genes that were more highly expressed in the root tip of the Al tolerant maize line under both +/-Al conditions and these genes will be the focus of future study. The candidate genes involve genes involved in cell wall synthesis, as well as genes involved in the release of citric acid, which when released from the maize root is believed to be complex and detoxify Al. This research should help us identify novel Al tolerance genes, and in turn, the discovery of Al tolerance genes will open up new avenues whereby plant breeders and biotechnologists can use this information to improve the acid tolerance of many crop species.
Technical Abstract: Aluminum (Al) toxicity is a major factor limiting crop yields on acid soils. Plant species exhibit considerable genotypic variation for Al tolerance, which is being exploited by researchers to identify the mechanisms that underlie this trait. In maize, Al tolerance is a complex phenomenon involving multiple genes and physiological mechanisms yet uncharacterized. To begin elucidating the molecular basis of maize Al toxicity and tolerance, we performed a detailed temporal analysis of root tip gene expression under Al stress using microarray analysis with Al-tolerant and Al-sensitive maize genotypes. Al altered expression of a significantly larger number of genes in the Al-sensitive genotype, presumably due to more severe Al toxicity. Nevertheless, several different categories of genes exhibited higher expression in the Al-tolerant genotype in response to Al. Cell wall-related genes exhibited strong differential expression under Al stress, and expression of low Pi-responsive genes was also found to be regulated by Al. Expression of genes related to Al-activated citrate release was also investigated, and indicated that in maize this mechanism is likely regulated by the expression level and/or function of the transporter. The present study is the first comprehensive survey of global root transcriptional regulation under Al stress. The results described here will help further our understanding of how Al toxicity influences gene expression and of how mechanisms of Al tolerance in maize are regulated at the transcriptional level.