Pathogen Identification of Raphanus sativus Phyllody Disease and the Expression Level of Key Enzyme Genes in GibberellinSynthesis and Metabolism Pathway

PurposeTo figure out the causal agent of Raphanus sativus phyllody disease occurred in Yuanmou of Yunnan Province and changes of expression level of key enzymes genes in gibberellin synthesis.

MethodThe phytoplasmal 16S rRNA gene sequence was amplified from total DNAs extracted from natural R. sativus plant showing phyllody, witches broom and shortened internodes symptoms. Then the amplicons were cloned, sequenced and phylogentic tree were constructed. Real-time fluorescence qualification RT-PCR was performed to detect changes of the expression level of key enzyme genes (GA20ox1, GA3ox1, GA2ox1) of gibberellin synthesis and metabolism pathway in this experiment.

ResultThe phytoplasma strain had the highest similarity of 0.98 with the phytoplasma subgroup 16SrII-A, and formed an evolutionary branch with other phytoplasma stranis which were classified in 16SrII-A subgroup.

ConclusionThe R. sativus phyllody phytoplasma (RsPh-YNym) strain belongs to phytoplasma 16SrII-A subgroup and is related to Candidatus phytoplasma aurantifolia. Meanwhile, we found that the expression levels of GA20ox1, GA3ox1 and GA2ox1 genes in the susceptible plants were down-regulated compared with the healthy plants and showed that the phytoplasma infection destroyed the homeostasis of gibberellin and changed the phenotypes of Raphanus sativus.