Resistant Response Of Maize To SO₂ Stress And Analysis Of Sulfite Oxidase Gene ZmSO In Maize（ Zea Mays L.）

Sulfur dioxide （SO₂） is the major air pollutants in China currently, which increasingly causes great harm to crop production, and has been becoming an important factor to limit yield and quality of crops. Sulfite oxidase （SO） as the member of the molybdenum enzymes’ family plays important roles in sulfur metabolism and detoxification of SO₂ gas toxicity in plants. Till now, researches on the plant SO have been focused on Arabidopsis thaliana or other dicotyledonous plants, lacking the report on SO from gramineae crops such as maize. In this study, by means of physiological, biochemical and molecular methods, we analyzed the resistance response of maize to SO₂ stress, and preliminary physiological function of maize SO using a transgenic technology. The main results are as follows:1. By SO₂ fumigation on eight maize inbred lines, we screened a highly resistant line Q319 and a highly susceptible line Chang7-2; Then using semi-quantitative RT-PCR, we studied the differential expression of 9 genes which were the adversity stress response genes （XERO, ERD, LEA）, antioxidant genes（SOD, CAT, APX, GST） and signal transduction genes（MAPK, RHB） under SO₂ stress in the resistant and susceptible maize lines. From that we found, comparing with those in high-susceptible line Chang7-2, the expression of the antioxidant genes SOD, APX, GST and the adversity stress response genes XERO, ERD, LEA were significantly increased in the highly resistant lines Q319. Under SO₂ stress, the research on the resistant differences in physiological and biochemical aspects about Q319 and Chang7-2 manifested that: in Q319 the accumulated amount of the hydrogen peroxide and superoxide ion and enzyme activity of SOD were significantly higher than in Chang 7-2; which implied that SOD played an important role in removing the reactive oxygen species produced in the process of SO₂ stress.2. The SO gene from maize was cloned by RT-PCR and RACE, we got the full-length sulfite oxidase （SO） cDNA, named ZmSO, was cloned from Q319. The cDNA contains a 1194bp open reading frame （ORF） and encodes 397 amino acids. Sequence alignment and structure prediction showed that the deduced amino acid sequence of ZmSO shared 72%, 74%, and 89% similarities with homologs from other plants such as Arabidopsis thaliana, Lycopersicon esculentum and Oryza sativa, respectively. In addition, similar to other plant SO homologs, ZmSO also contained three conserved functional domains such as one Moco-binding domain, one dimerization domain and one peroxisome targeting signal. Also its expression was analyzed under SO₂ stress using semi-quantitative RT-PCR method; still to use the maize inbred lines of Q319 and Chang 7-2 for comparison, the expression of the gene ZmSO in Q319 was clearly higher than in Chang 7-2.3. Using virus-induced gene over-expression system to instantaneously express ZmSO in tabacum benthamiana, we found that SO activity in ZmSO transgenic plant was significantly higher than that in control plants. At 3mM and 5mM sulfite treatments, the leaves of ZmSO transgenic plants were slightly injured, and the chlorophyll content was significantly higher than the control group, which proofed that ZmSO had a sulfite-detoxification function. In addition, a 35S promoter-driven SO expression vector had been constructed and transformed into N. tabacum Xanthi. The transgenic tobacco plants have been obtained by molecular detection, which laid the base for further studying the regulatory mechanism of ZmSO in sulfite-detoxification in plants.