2013 Annual Report
1a.Objectives (from AD-416):
The objectives of this cooperative research project are to increase our understanding of mechanisms of aluminum tolerance, heavy metal transport, and nutritional quality and health-promoting properties of plants.
1b.Approach (from AD-416):
1) A combination of joint-association mapping, comparative genomics, and biochemistry approaches will be used to study aluminum tolerance genes we recently cloned in wheat, sorghum and maize from the ALMT and MATE gene families. The research on sorghum and maize involves collaborative research with Embrapa Maize and Sorghum in Sete Lagoas, Brazil. The research on rice involves collaborative research with South China Agricultural University, Guangzhou, China, and Zhejiang University, Huangzhou, China. The information will be used to enhance acid soil tolerance of cereal crops, with a focus on sorghum, maize and rice. .
2)The molecular physiology of heavy metal transport will be studied in the heavy metal hyperaccumulator, Thlaspi caerulescens. We have identified a number of genes that are candidates for involvement in metal hyperaccumulation in Thlaspi and will study them in more detail to determine if they are indeed, hyperaccumulation genes. These will be used via biotechnology to improve plants for use in remediation of metal-contaminated soils. .
3)Recently identified QTL that enhance Fe bioavailability in maize seed will be characterized and a combined genomic, genetic and metabolic approach will be employed to identify the genes underlying the QTL as well as the secondary compounds underlying the FE bioavailability.
Progress for this project in 2013 involved continued research on sorghum and rice aluminum tolerance, which is an important agronomic trait for crops grown on acid soils that are prevalent in the US and the rest of the world, especially in developing countries. On acid soils, Al ions are dissolved into the soil solution and are toxic to and damage plant roots, thus greatly reducing crop vigor and yields. This research is based on our previous discovery of the major sorghum gene (SbMATE) that controls most of the tolerance to aluminum (Al) toxicity in sorghum. We have identified a novel protein that binds to and regulates SbMATE making it very efficient at the release of citrate acid, which SbMATE transports out of roots into the soil where it binds to and detoxifies Al ions. We call this protein SbMBP, for Sorghum bicolor MATE binding protein. In this year we investigated the details of the interaction between the SbMATE primary Al tolerance protein and SbMBP. We discovered that SbMBP is an Al binding protein. When the root is grown in soil where there are low levels of toxic Al ions, the SbMBP protein binds tightly to the SbMATE protein, and blocks citrate efflux by SbMATE. When roots grow into an acid soil containing toxic levels of Al ions, the Al enters the root cell and binds to SbMBP. This causes the SbMBP protein to come off SbMATE allowing citrate to be released into the soil, where it detoxifies Al ions, allowing the root to grow. We found that the binding of SbMBP to SbMATE blocks citrate transport and that SbMBP is an Al sensor and when it binds Al ions, it is released from the SbMATE protein, allowing the transport of citrate out of the root. This regulation of SbMATE ensures that unnecessary carbon loss from the root does not occur under non-Al toxic conditions, as citrate release from the root is a significant cost to the plant. In collaboration with Embrapa Maize and Sorghum, Brazil, we are using these findings to improve productivity of sorghum grown as a major food crop in sub-Saharan Africa and investigating the possibility to increase the productivity of biofuel sorghum grown on acid soils prevalent in the southeastern U.S.