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We are pleased to announce that Dr Sun Xuecheng has been awarded the Annals of Botany Graduate Prize for a paper published in the second half of 2009 reporting work from a thesis. His paper ‘Effects of molybdenum on expression of cold-responsive genes in abscisic acid (ABA)-dependent and ABA-independent pathways in winter wheat under low-temperature stress’ (Sun et al., 2009) brings new understanding of the genes and the genetic pathways involved in cold resistance related to Mo application. Xuecheng carried out this work in a research group at the Center of Trace Elements, Huazhong Agricultural University, Wuhan, China. The motivation for the work came from the late 1980s, when the group showed that Mo deficiency was a major factor causing leaf-yellowing, tiller death and decreased yields of winter wheat in Xinzhou, Hubei Province, China. After several years of field and pot experiments, the technology of Mo-fertilizer application to winter wheat was established and the yield of wheat was increased by 20–30 % in Mo-deficiency areas such as Hubei and Henan Province. Field and pot experiments showed that low-temperature stress can accelerate the development of Mo-deficiency symptoms, and application of Mo enhanced the cold-resistance of winter wheat.
The objective of Xuecheng's PhD work was to obtain new insights on the physiological and molecular mechanisms of cold resistance arising from application of Mo in winter wheat, and to answer why or how molybdenum controls the plant cold resistance. He first confirmed that freezing tolerance in Mo-fertilized wheat was enhanced, and showed differences between Mo-efficient and Mo-inefficient lines, and then focused on the biological and metabolic processes related to Mo-enzymes. This required a broad study, since there are effects of molybdenum on not only Mo-enzymes, but through hormones, antioxidative enzymes, expression of cold-responsive (COR) genes, the composition of thylakoids and photosynthetic parameters. These were investigated in winter wheat by a wide range of biochemical methods combined with real-time PCR, two dimensional electrophoresis and mass spectrometry. The paper concludes that Mo might regulate the expression of ABA-dependent COR genes through the pathway: Mo → AO → ABA → bZIP → ABA-dependent COR genes in winter wheat. The response of the ABA-dependent pathway to Mo was prior to that of the ABA-independent pathway. Unpublished quantitative proteomics data showed that most of differential proteins were located in membrane of thylakoids, and their functions were closely related to light reactions and dark reactions of photosynthesis. The results of COR gene expression and differential proteins were also supported by the results concerning composition of thylakoids and photosynthetic parameters. So a mechanism was initially put forward: molybdenum regulated the gene expression via Mo-enzymes, and then successively affected the protein expression, metabolic processes, physiological functions such as enhancing the photosynthesis, and cold resistance in winter wheat.
Since graduating, Xuecheng has become a lecturer in Huazhong Agricultural University, and is continuing research work on plant molybdenum nutrition. Since most of the differential proteins were located in membrane of thylakoids, and the chloroplast is centre of photosynthetic carbon and nitrogen metabolism, he is trying to clarify the role of molybdenum in the integration of photosynthetic carbon and nitrogen metabolism in higher plants. He is also interested in the mechanisms of uptake, translocation and metabolism of other microelements in plants, especially at the proteome and metabolome level. In the future, Xuecheng hopes to establish collaboration in this work with other leading research laboratories.