Gene structure and expression pattern analysis of three monodehydroascorbate reductase (Mdhar) genes in Physcomitrella patens: Implications for the evolution of the MDHAR family in plants

The original publication can be found at www.springerlink.comThe ascorbate–glutathione pathway plays a major role in the detoxification of reactive oxygen species (ROS) in vascular plants. One of the key enzymes in this pathway is monodehydroascorbate reductase (MDHAR), a FAD enzyme that catalyses the reduction of the monodehydroascorbate radical. To elucidate the evolution and functional role of MDHAR we identified and characterised MDHARs from the moss Physcomitrella patens. Expressed sequence tag (EST) databases containing approximately 100.000 ESTs from Physcomitrella were searched and three isoforms of monodehydroascorbate reductase (PpMDHAR1, PpMDHAR2 and PpMDHAR3) were identified. In vascular plants MDHAR is found in the cytosol, chloroplast, mitochondria and peroxisome. Surprisingly, all three PpMDHARs resembled the cytosolic isoforms from vascular plants lacking the NH ₂-terminal or COOH-terminal extension found in organelle targeted MDHARs. The number and position of introns was also conserved between PpMDHARs and cytosolic MDHARs from vascular plants. Phylogenetic analysis revealed that cytosolic MDHARs are monophyletic in origin and the ancestral gene evolved before the divergence of bryophytes more than 400 million years ago. Transcript analyses showed that expression of PpMdhar1 and PpMdhar3 was increased up to 5-fold under salt stress, osmotic stress or upon exposure to abscisic acid. In contrast, PpMdhar transcription levels were unchanged upon chilling, UV-B exposure or oxidative stress. The conservation of cytosolic MDHAR in the land-plant lineage and the transcriptional upregulation under water deficiency suggest that the evolution of cytosolic MDHAR played an essential role in stress protection for land plants when they inhabited the dry terrestrial environment.Christina Lunde, Ute Baumann, Neil J. Shirley, Damian P. Drew and Geoffrey B. Finche

Genomics of tolerance to abiotic stress in the Triticeae

Genomics platforms offer unprecedented opportunities to identify, select and in some cases clone the genes and the quantitative trait loci (QTLs) that govern the tolerance of Triticeae to abiotic stresses and, consequently, grain yield. Transcriptome profiling and the other \u201comics\u201d platforms provide further information to unravel gene functions and validate the role of candidate genes. This review provides a synopsis of the main results on the studies that have investigated the genomics of Triticeae crops under conditions of abiotic constraints. With their rich biodiversity and high functional plasticity in response to environmental stresses, Triticeae crops provide an ideal ground for taking full advantage of the opportunities offered by genomics approaches. Ultimately, the practical impact of the knowledge and materials generated through genomics-based approaches will depend on their integration and exploitation within the extant breeding programs