Abstract
There are 25 auxin response factors (ARFs) in the rice genome, which play critical roles in regulating myriad aspects of plant development, but their role (s) in host antiviral immune defense and the underneath mechanism remain largely unknown. By using the rice-rice dwarf virus (RDV) model system, here we report that auxin signaling enhances rice defense against RDV infection. In turn, RDV infection triggers increased auxin biosynthesis and accumulation in rice, and that treatment with exogenous auxin reduces OsIAA10 protein level, thereby unleashing a group of OsIAA10-interacting OsARFs to mediate downstream antiviral responses. Strikingly, our genetic data showed that loss-of-function mutants of osarf12 or osarf16 exhibit reduced resistance whereas osarf11 mutants display enhanced resistance to RDV. In turn, OsARF12 activates the down-stream OsWRKY13 expression through direct binding to its promoter, loss-of-function mutants of oswrky13 exhibit reduced resistance. These results demonstrated that OsARF 11, 12 and 16 differentially regulate rice antiviral defense. Together with our previous discovery that the viral P2 protein stabilizes OsIAA10 protein via thwarting its interaction with OsTIR1 to enhance viral infection and pathogenesis, our results reveal a novel auxin-IAA10-ARFs-mediated signaling mechanism employed by rice and RDV for defense and counter defense responses.
Highlights
Rice is a major staple crop feeding more than half of world’s population [1]
We previously showed that Rice dwarf virus (RDV) infection stabilizes OsIAA10 protein and that knocking down OsIAA10 expression in rice causes enhanced resistance to RDV infection [12], suggesting that auxin signaling plays a positive role in rice antiviral defense
We measured the IAA content in healthy and RDV infected rice, and found that the auxin accumulation is higher in RDV-infected rice (Fig 1A). quantitative real-time PCR (qRT-PCR) analysis showed that many auxin biosynthesis genes were up-regulated in RDV-infected rice, such as YUCCA6, TRPC, YUCCA8, AAO2, AAO1, TSA1, TRP1, and TRP4 (Fig 1B)
Summary
Rice is a major staple crop feeding more than half of world’s population [1]. Viral infection causes enormous losses in rice yield and quality, posing a constant threat to global food security [1,2,3]. Rice dwarf virus (RDV), a member of the genus Phytoreovirus in the family Reoviridae transmitted by leafhoppers (Nephotettix cincticeps), is a major threat to rice production in Asia [6,7,8,9]. RDV infection disturbs the normal physiology and metabolism of rice, leading to dwarfism, production of excess tillers, dark green leaves with white chlorotic specks, delayed maturation, higher rate of abortive grains, and reduced grain yield with deteriorated quality [12,13,14,15]
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