Abstract: 【Objective】 In recent years, wheat dwarf virus disease transmitted by leafhopper (Psammotettix alienus) is becoming one of the severe virus disease on triticeae crops in the northwest of China. Infected plants may be severely dwarfed and reduced effective tillering so that it causes serious production loss. The objectives of this study are to clear the correlation between dwarfing of plant height induced by Wheat dwarf virus (WDV) infection and gibberellin metabolism and provide a solid basis for the control of the disease. 【Method】The cultivar Yangmai 12 was used as experimental material. Leafhoppers were fed on viruliferous wheat containing WDV and then transferred to healthy seedling at single-leaf stage (3 heads/plant). The leaves were collected as samples at different time points according to experimental requirements and the seedlings treated with non-viruliferous leafhoppers as control. To guarantee the accuracy of the experiment, all the infected samples were validated by PCR. The plant GA3 ELISA Kit was used to assay the GA3 contents of both healthy and WDV-infected wheat leaves at 21 days post-infection (dpi). Viruliferous treatments were divided into two parallel groups, one was treated with spraying of exogenous GA3 at 50 mg·L^-1 and the other treated with water at 7 dpi. The spraying of GA3 solution was carried out 4 times every 7 days. Meanwhile, the control group consisted of similar size seedlings were treated with non-viruliferous leafhoppers. The phenotype was analyzed by statistical analysis of the plant heights after application of exogenous GA3 at 50 mg·L^-1. According to the coding sequence of ent-kaurene synthase-like 3 (KSL3) of Aegilops tauschii for reference, the complete coding sequence of KSL3 of Yangmai 12 was cloned with the primer pair (KSL3-F: 5′-ATGATGGTGAATCCGCCGC-3′, KSL3-R: 5′-TTAATGGTTGATCTTTGTTT-3′) and its structure was analyzed with BLAST. The total RNA of infected plants at 7, 14 and 21 dpi were prepared and reversed transcription into cDNA. The primers were designed following the obtained sequence of TaKSL3 (TaKSL3-F: 5′-GAGACATGTGCCATGGCGTTC-3′, TaKSL3-R: 5′-CGTGTCACTC AGATCGGTGGAG-3′). With EF-1α as the reference gene, RT-qPCR was used to analyze the expression level of gene related to GA metabolism pathway.【Result】The GA3 content of infected plants was reduced by 28.9% at 21 dpi by indirect ELISA and the height of infected plants increased by 35.9% owing to application of exogenous GA3 at 50 mg·L^-1 compared with control. Using homology-based cloning, the complete coding sequence of Yangmai 12 KSL3 was obtained, which is the key enzyme in gibberellin synthesis pathway. The sequence of KSL3 has the length of 1 827 bp, encoding 608 amino acids. By BLAST analysis, its DNA sequence was found to have a similarity of 85.2% compared with KSL3 of A. tauschii. Particularly, by qRT-PCR analysis, the expression level of KSL3 compared to healthy plants significantly decreased to 35.7% at 14 dpi and 9.6% at 21dpi, respectively.【Conclusion】 It was concluded that WDV could interfere the biosynthesis of GA leading to the decreased content of GA, which was responsible for the development of dwarf symptom that can be relieved by exogenous GA. This study will provide a solid basis for further research on pathogenesis of WDV and control of the disease.

Key words: Wheat dwarf virus (WDV), dwarfing, gibberellin, ent-kaurene synthase, pathogenesis