Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: June 14, 2013
Publication Date: October 11, 2013
Repository URL: http://onlinelibrary.wiley.com/doi/10.1002/9781118728482.ch6/summary
Citation: Magalhaes, J.V., Maron, L.G., Pineros, M., Guimaraes, C.T., Kochian, L.V. 2013. Aluminum tolerance in sorghum and maize. In: Varshney, R., Ruberosa, R., editors. Translational genomics for crop breeding: improvement for abiotic stress, quality and yield improvement. Volume 2. Chichester, UK. Wiley and Sons Ltd. p. 83-98. DOI: 10.1002/9781118728482.ch6 Technical Abstract: The soils of the tropics and subtropics are highly weathered, leading to poor soil fertility and low soil pH. Root growth and function on these acid soils is impaired by aluminium (Al) toxicity, leading to yield instability that jeopardizes food security worldwide. A wealth of physiological evidence exists for an Al tolerance mechanism based on Al exclusion from the growing root tip. This is facilitated by the release of Al-binding organic acids such as malate and citrate, which keeps rhizotoxic Al away from sensitive sites in the root apex. More recently, Al-activated organic acid transporters in the ALMT and MATE protein families have been cloned and provide the molecular support for this Al tolerance mechanism. Here a historical review of Al tolerance in maize and sorghum is presented, followed by an analysis of the more recent research on the molecular determinants of Al tolerance. We show that Al tolerance provided by MATE proteins spans the genetic divergence between sorghum and maize, and is a conserved physiological mechanism in both species. Some features of this mechanism are strikingly common in sorghum and maize, such as the close relationship between phenotypic variation and MATE gene expression. However, while the genetic basis for maize aluminium tolerance is quantitative, in sorghum SbMATE underlies the major Al tolerance locus. More subtle features of this Al tolerance trait are now emerging, such as the importance of trans-acting factors in sorghum, whereas Al tolerance gene expression in maize appears to be predominantly controlled in cis. Knowledge of the molecular basis of Al tolerance is now providing the framework to address pivotal historical questions in the field, such as the occurrence of genetic background effects for aluminium tolerance. We advocate here that the answer to such questions will inevitably form the basis for modern molecular breeding strategies designed to explore in full the potential for genetic solutions to the Al tolerance problem for crops grown on acid soils.