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POSTERS: Plant defense response

OsSPL9 regulates rice antiviral response through the miR528-L-ascorbate oxidase (AO) pathway
Shengze Yao - School of Life Sciences, Peking University. Zhirui Yang- School of Life Sciences, Peking University, Yi Li- School of Life Sciences, Peking University

MicroRNAs (miRNAs) are critical regulators of plant antiviral defense. However, little is known as to how miRNAs respond to virus invasion on transcriptional level. We established previously that defense to Rice stripe virus (RSV) invasion entailed a reduction of miR528 accumulation in rice due to the down-regulation on transcriptional level, thus alleviating miR528-mediated degradation of L-Ascorbate Oxidase (AO) mRNA, bolstering the antiviral activity of AO. Here we show that a large number of GTAC motifs existed on the promoter of miR528, which was considered as the binding site of SQUAMOSA Promoter Binding Protein–Like (SPL) transcription factor family protein. To investigate which SPL transcriptional factor regulates the transcription of miR528, we used Yeast one hybrid and other technique, and show that miR528 is regulated by the SPL9 specifically among 19 SPLs in rice. SPL9 displayed high affinity binding to specific motifs within the promoter region of miR528 and activated the transcription of miR528 promoter in vivo and in vitro. To confirm our hypothesis, we obtained SPL9 overexpression and knock out mutant (Crispr/Cas9) rice lines. Knock-out spl9 significantly reduces the expression of miR528, but increasing the expression of the target of miR528, AO expression and rice resistance to RSV, while overexpression of SPL9 increases the expression of miR528, but reduces the expression of AO and host antiviral defense. In conclusion, SPL9-mediated transcriptional activation of miR528 expression adds a novel layer of regulation of miR528-AO antiviral defense.