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Oral: Effector Biology


Dissecting the function and downstream targets of CsLOB1 in citrus
S. DUAN (1), H. Jia (1), S. Gowda (1), N. Wang (1) (1) Citrus research and education center, U.S.A.

Citrus canker caused by Xanthomonas citri pv. citri (Xcc) is a devastating disease affecting most citrus species. PthA4, one of Xcc Type III secretion system effectors, is responsible for citrus canker pustule formation on citrus leave. PthA4 binds to the effector binding element in the promoter of CsLOB1 to activate its gene expression, which subsequently activates genes responsible for pustule formation. CsLOB1 has not been functionally characterized and it remains unknown how CsLOB1 controls its downstream genes. CsLOB1 was highly expressed in the citrus stem phloem and cambial zone in wild-type plants. We aim to study the function of CsLOB1 and identify the putative downstream target genes of CsLOB1. To observe the physiological effect by suppressing CsLOB1 expression, a Citrus Tristeza Virus-based RNAi vector, engineered with truncated anti-sense CsLOB1, was constructed for Virus-induced Gene Silencing (VIGS). Suppression of CsLOB1 via VIGS caused decreased stem diameter and retarded plant growth. To further confirm this result, Agrobacterium-mediated transient gene expression method is being used to reveal the CsLOB1 function during pustule formation post Xcc infection on citrus leave using small hairpin (shRNA) and artificial microRNA methods. Meanwhile, Dexamethasone-inducible CsLOB1 over-expression transgenic plants were constructed to identify the putative downstream genes of CsLOB1.