Submitted to: American Phytopathological Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/9/2016
Publication Date: 8/3/2016
Citation: Hao, G., Pitino, M., Ammar, E., Duan, Y., Stover, E.W. 2016. Transgenic Carrizo expressing 'Candidatus Liberibacter asiaticus' effector P235 displays huanglongbing-like symptom and alters some gene expression [abstract]. American Phytopathological Society Abstracts, July 30 - August 1, 2016, Tampa, Florida.
Technical Abstract: ‘Candidatus Liberibacter asiaticus’ (Las) is the agent causing destructive citrus huanglongbing worldwide. A hypothetical protein (P235) was identified in Las genome prophage region, which encodes a 123aa protein with a molecular weight of 14.19kD. Green fluorescence protein (GFP)-fused with P235 appeared to accumulate in Nicotiana benthamiana cell nuclei by Agrobacterium-mediated transient expression, however, P235-GFP fusion protein in transgenic citrus targets the citrus chloroplast. P235 alone was constructed into a binary vector for citrus transformation. Over 40 independent transgenic Carrizo were obtained. Gene integration and gene expression was confirmed by molecular analysis. We observed that some P235-expressing Carrizo plants displayed huanglongbing-like symptoms with leaf chlorosis and plant growth retardation. P235 expression levels, determined by reverse transcription quantitative polymerase chain reaction (RT-qPCR), correlated with huanglongbing-like symptoms. Transcriptome analysis showed carbohydrate metabolism and biotic stress pathways were significantly affected in transgenic citrus expressing p235 effector. Gene expression were highly upregulated for several stress-related genes involved in hormone metabolism and zinc ion binding. Phloem protein 2-like (PP2-B15-like), which was reported to be induced in huanglongbing (HLB) infected sweet orange, was highly suppressed in transgenic plants expressing p235. This is the first report that ‘Candidatus Liberibacter asiaticus’ encodes a protein that targets the chloroplast of plant cells and alters plant host phenotypes.