Multiple types of markers including SSR, RFLP and SNP were developed to trace the interesting genes. These markers provide not only efficient tools for genetic studies but also important Etoposide resources for molecular marker-assisted selection. Marker-assisted selection has shifted from linked markers to gene-specific molecular markers for direct tracing of genes of interest. Gene-specific markers developed from wheat Al tolerance gene TaALMT1

and barley Al tolerance gene HvAACT1 co-segregate with the respective tolerance genes and thus should be efficient in MAS [148] and [158]. As shown in Fig. 5, the gene-specific marker HvMATE-21indel can be used to differentiate tolerant and sensitive barley cultivars. Genetic behavior of the tolerance of some plant species has been clarified with some genes responding for Al tolerance being identified. In some genotypes of barley [141], wheat [140], and maize [142], gene expression was reportedly affected by variation in gene sequence. However, regulatory networks affecting gene expression remain poorly understood. The future challenge for studying Al tolerance is the identification of new tolerance mechanisms. For example, it was reported that citrate exudation is the main mechanism and HvAACT1 is the responsible Ku-0059436 cell line gene for Al tolerance in barley. However, as shown in Fig. 6, the gene-specific marker based on the 1 kb InDel does not differentiate Tyrosine-protein kinase BLK tolerant

cultivars from sensitive ones [148]. The function

of the other gene, HvALMT1, for malate acid exudation in barley is still unclear. Due to recent advances in marker development, a stronger impact of marker-assisted selection in breeding is expected. Although MAS is used successfully for Al tolerance, current markers are still some distance from the Al-tolerance genes. Closer markers or gene-specific markers will make selection more efficient. Combinations of different tolerance mechanisms may achieve better tolerance, thus the discovery of new genes remains a priority for improved Al tolerance in crop plants. This study was supported by the Australian Grains Research and Development Corporation. “
“Many important crops including rice (Oryza sativa L.), wheat (Triticum aestivum L.), soybean (Glycine max L.), and potato (Solanum tuberosum L.) are classified as C3 plants, in which the first product of the Calvin cycle is 3-phosphoglycerate (3-PGA), whose production is catalyzed by ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco). However, competition of O2 with CO2 at the catalytic site of Rubisco results in a loss of up to 50% of carbon fixation via photorespiration [1]. Compared with C3 plants, C4 crops such as maize (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench] have evolved a C4-metabolism system that concentrates CO2 in the vicinity of Rubisco and thereby substantially increases the ratio of RuBP carboxylation to oxygenation.