Location: Plant, Soil and Nutrition ResearchTitle: The relationship between population structure and aluminum tolerance in cultivated sorghum Author
|Garcia, Antonio Augusto|
|Oliveira, Antonio Carlos|
Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2011
Publication Date: 6/14/2011
Citation: Caniato, F., Guimaraes, C., Hamblin, M., Billot, C., Rami, J., Maciel, B.H., Kochian, L.V., Liu, J., Garcia, A., Hash, C.T., Ramu, P., Mitchell, S., Kresovich, S., Oliveira, A., Avelar, G., Borem, A., Glaszmann, J., Schaffert, R.E., Magalhaes, J.V. 2011. The relationship between population structure and aluminum tolerance in cultivated sorghum. PloS One. 6(6):e20830. DOI: 10.1371/journal.pone.0020830. Interpretive Summary: Over 20 percent of the U.S. land area and approximately 50 percent of the world’s arable lands are acidic (pH < 5). On these acid soils, aluminum (Al) toxicity is the primary factor limiting crop production as Al is toxic to plant roots, leading to a damaged and stunted root system. As a large proportion of the acid soils are in the tropics/subtropics where many developing countries are located, Al toxicity limits crop production in the very areas where food security is most tenuous. Because of the importance of this problem to agriculture worldwide, there is considerable interest and research effort by researchers at universities, government agencies, and international agriculture organizations in identifying genes that provide tolerance to Al toxicity in order to improve crop Al tolerance via molecular breeding and biotechnology. One of the major physiological mechanisms for crop plants to cope with Al stress involves the efflux of organic acids (OA) from roots. The released organic acids detoxify Al by forming a non-toxic organic acid-Al complex. We had previously identified the major Al tolerance gene in sorghum, an important food crop in Africa and important animal feed and biofuel crop in the US. This gene, named SbMATE, encodes a transporter that releases the strong Al chelator, citric acid, from the root tips, protecting the growing root tip from toxic Al in the soil. In this study we conducted a genetic analysis of Al tolerance controlled by this SbMATE gene in 254 sorghum lines that capture most of the variation in sorghum Al tolerance. We found that sorghum Al tolerance is a rare event. We also found that due to domestication, sorghum can be divided into a number of different subpopulations and Al tolerance is only found in 1-2 of these subpopulations. Furthermore, we found that how SbMATE functions as an Al tolerance gene is influenced by this subpopulation structure. These findings will be useful for sorghum breeders to help direct their breeding programs for improved Al tolerance on acid soils.
Technical Abstract: Acid soils comprise up to 50% of the world’s arable lands and in these areas aluminum (Al) toxicity impairs root growth, strongly limiting crop yield. Food security is thereby compromised in many developing countries that are located in tropical and subtropical regions worldwide. In sorghum, SbMATE, an Al-activated citrate transporter, underlies the AltSB locus on chromosome 3 and confers Al tolerance via Al-activated root citrate release. Population structure was studied in 254 sorghum accessions representative of the diversity present in cultivated sorghums. Al tolerance was assessed as the degree of root growth inhibition in nutrient solution containing Al. A genetic analysis based on AltSB marker and SbMATE expression analysis were undertaken to assess a possible role for AltSB in Al tolerant accessions. In addition, the mode of gene action was estimated concerning the Al tolerance trait. Comparisons between models that include population structure were applied to assess the importance of each subpopulation to Al tolerance. Six subpopulations were revealed featuring specific racial and geographic origins. Al tolerance was found to be rather rare and present primarily in guinea and to lesser extent in caudatum subpopulations. AltSB was found to play a role in Al tolerance in most of the Al tolerant accessions. A striking variation was observed in the mode of gene action for the Al tolerance trait, which ranged from partial recessivity to partial dominance, with a higher frequency of partially recessive sources of Al tolerance. This study demonstrates the importance of a deep exploration of the crop diversity reservoir both for a more comprehensive view of the dynamics underlying the distribution and function of Al tolerance genes and to design efficient molecular breeding strategies aimed at enhancing Al tolerance.