Aldehyde Dehydrogenase Gene Superfamily in Populus: Organization and Expression Divergence between Paralogous Gene Pairs.

Aldehyde dehydrogenases (ALDHs) constitute a superfamily of NAD(P)+-dependent enzymes that catalyze the irreversible oxidation of a wide range of reactive aldehydes to their corresponding nontoxic carboxylic acids. ALDHs have been studied in many organisms from bacteria to mammals; however, no systematic analyses incorporating genome organization, gene structure, expression profiles, and cis-acting elements have been conducted in the model tree species Populus trichocarpa thus far. In this study, a comprehensive analysis of the Populus ALDH gene superfamily was performed. A total of 26 Populus ALDH genes were found to be distributed across 12 chromosomes. Genomic organization analysis indicated that purifying selection may have played a pivotal role in the retention and maintenance of PtALDH gene families. The exon-intron organizations of PtALDHs were highly conserved within the same family, suggesting that the members of the same family also may have conserved functionalities. Microarray data and qRT-PCR analysis indicated that most PtALDHs had distinct tissue-specific expression patterns. The specificity of cis-acting elements in the promoter regions of the PtALDHs and the divergence of expression patterns between nine paralogous PtALDH gene pairs suggested that gene duplications may have freed the duplicate genes from the functional constraints. The expression levels of some ALDHs were up- or down-regulated by various abiotic stresses, implying that the products of these genes may be involved in the adaptation of Populus to abiotic stresses. Overall, the data obtained from our investigation contribute to a better understanding of the complexity of the Populus ALDH gene superfamily and provide insights into the function and evolution of ALDH gene families in vascular plants.

The antioxidative defense system is involved in the delayed senescence in a wheat mutant tasg1.

Wheat, which is the most important food crop worldwide, is a cereal that presents considerable potential for increased yield. A new wheat (Triticum aestivum L.) mutant tasg1 with delayed leaf senescence was constructed using ethyl methane sulfonate as a mutagen. Natural senescence in tasg1 was distinctly delayed in the field, as indicated by the slower progression of chlorophyll degradation, net photosynthetic rate than its wild type. Further, the malondialdehyde and the hydrogen peroxide content was lower and antioxidative enzyme activity higher in tasg1 than those in its wild type during both natural senescence and methyl viologen-induced oxidative stress. The results suggest that tasg1 is a functional stay-green wheat mutant with the Type B (in which senescence initiates on schedule, but progresses at a rate lower than that in the respective WTs) or Type A (in which senescence initiates late but proceeds at a normal rate) and B combination and that the competence of the antioxidant defense system is one of the most important mechanisms underlying the expression of the stay-green phenotype.

[Runoff and sediment processes and anti-erosion effects of grass-covered earth road in loess hilly region].

A laboratory simulation test with slope-adjustable steel tank and artificial rainfall was conducted to study the runoff and sediment processes of uncovered and Poa pratensis L.-planted earth roads, and the anti-erosion effects of P. pratensis-planted earth road. At the same rainfall intensity and slope, the runoff coefficient of P. pratensis-planted earth road was larger than that of uncovered earth road. For the two kinds of earth roads, their runoff coefficients all increased with increasing rainfall intensity and slope. At the same slope but different rainfall intensity, the runoff coefficient had a logarithmic relationship with rainfall duration, and a quadratic relationship with slope or rainfall intensity. Soil erosion rate increased with increasing rainfall intensity or slope, and was smaller on the P. pratensis-planted earth road at the same rainfall intensity. The average antierosion efficacy of P. pratensis-planted earth road was 47.22% at different rainfall intensity, and was 26.24% at different slope. Because of its higher roughness and higher road surface resistance coefficient, P. pratensis-planted earth road had a lower sediment yield and a decreased sediment transport.