A role for chloroplast-localized Thylakoid formation 1 (THF1) in bacterial speck disease development

Abstract

Coronatine (COR), a jasmonate mimic produced by Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) is required for full virulence of Pst DC3000 in tomato and Arabidopsis. COR is shown to induce a range of physiological processes including chlorosis, root growth inhibition and anthocyanin accumulation in tomato. To elucidate the host/signaling genes involved in COR-responses, we utilized a forward genetics approach using Nicotiana benthamiana and virus-induced gene silencing (VIGS) and identified genes that play a role in COR-mediated chlorosis. We designated these genes as altered COR response (ALC). When silenced, one gene designated ALC1 produced a hypersensitive/necrosis-like phenotype after COR application in a coronatine insensitive 1 (COI1)-dependent manner. In pathogenicity assays performed on Arabidopsis thylakoid formation 1 (thf1) knockout lines and SlALC1-silenced tomato plants, Pst DC3000 induced coalescing necrotic lesions in an accelerated manner. Furthermore, we showed that COR affects ALC1 localization in chloroplast in a COI1-dependent manner. In conclusion, our results show the potential of VIGS-based, forward genetic screens to identify new players in COR-mediated signal transduction.

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Acknowledgements

This work was supported by the Samuel Roberts Noble Foundation and in part by a grant to S.R. Uppalapati from Oklahoma Center for Advancement of Science and Technology (PSB09-021). C.L. Bender acknowledges financial support from National Science Foundation grant (IOB-0620469). A spinning disk confocal microscope was purchased by an equipment grant from NSF (DBI-0722635).

Figures and Tables

Figure 1 Senescence-associated SAG12 expression in thf1 mutants in response to Pst DC3000. Transcripts of SAG12 were quantified by real time quantitative PCR in wild-type (Col-0, black bars) and thf1 mutant (open bars) lines of Arabidopsis after Pst DC3000 inoculation. Four-week old plants of Col-0 and the thf1 mutant were syringe-infiltrated with either Pst DC3000 (10⁶ CFU/ml) or buffer (mock control). The transcript levels were quantified relative to the transcript levels on mock control, which was assigned a value of 1.

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