Poster abstracts
Poster number 93 submitted by Huazhen Liu
Involvement of the plant polyadenylation factors FIP1 and CPSF30 in immune responses
Huazhen Liu (Department of Plant Pathology, University of Kentucky), Lichun Zhu (Department of Plant and Soil Sciences, University of Kentucky), Pradeep Kachroo (Department of Plant Pathology, University of Kentucky), Arthur G. Hunt (Department of Plant and Soil Sciences, University of Kentucky)
Abstract:
In plants, Systemic Acquired Resistance (SAR) is a form of systemic immunity that protects uninfected parts of a pathogen-inoculated plant against further disease. In a previous study, it was shown that a novel plant polyadenylation factor subunit, CPSF30, is required for resistance against a bacterial pathogen (1). The Arabidopsis thaliana ortholog of the yeast polyadenylation complex subunit Fip1p, FIP1, associates with the Arabidopsis ortholog of CPSF30 in vitro (2, 3). This association raises the possibility that the two proteins may work as a unit, and thus that Arabidopsis FIP1 may also play roles in defense responses. To test this in the context of SAR, we treated a set of mutant and complemented Arabidopsis lines with an avirulent strain of Pseudomonas syringae to induce SAR. The set of lines included a mutant (fip1-1) that does not express FIP1, a line in which the FIP1 gene is over-expressed in the fip1-1 mutant background, an additional mutant (oxt6) that does not express CPSF30, and a line that expresses CPSF30 in the oxt6 background. The results show that lines that express FIP1 or CPSF30 can establish an SAR, but lines that do not express FIP1 or CPSF30 are deficient in SAR. All of the wild type, mutant, and transgenic plants have similar transcriptional responses in the inoculated leaf to the avirulent pathogen. However, they differ in the (immune) distal leaves, and the differences relate to the well-established transcriptional response in SAR. We conclude that FIP1 and CPSF30 act downstream from the initial challenge by the avirulent pathogen and outside of the inoculated leaf. Interestingly, the fip1-1 and oxt6 mutants show altered poly(A) site usage of non-coding RNAs encoded by the TAS3a locus. The non-coding RNA TAS3a is a precursor for tasi-RNAs D7 and D8, which are early mobile signals for SAR (4). TAS3a transcripts undergo alternative polyadenylation, and poly(A) site choice affects the ability to generate the D7 and D8 tasi-RNAs. The observed changes in TAS3a poly(A) site usage in the fip1-1 and oxt6 mutants preclude production of the D7 and D8 tasi-RNAs. We propose that FIP1/CPSF30-dependent usage of the distal TAS3a poly(A) site is the mechanism that links FIP1/CPSF30 with SAR. Taken together, these studies provide new insights into the connections between mRNA polyadenylation and the plant immune system.
References:
1. Q. Bruggeman et al., The Polyadenylation Factor Subunit CLEAVAGE AND POLYADENYLATION SPECIFICITY FACTOR30: A Key Factor of Programmed Cell Death and a Regulator of Immunity in Arabidopsis. Plant Physiol 165, 732-746 (2014).
2. B. Addepalli, A. G. Hunt, A novel endonuclease activity associated with the Arabidopsis ortholog of the 30-kDa subunit of cleavage and polyadenylation specificity factor. Nucleic Acids Res 35, 4453-4463 (2007).
3. K. P. Forbes, B. Addepalli, A. G. Hunt, An Arabidopsis Fip1 homolog interacts with RNA and provides conceptual links with a number of other polyadenylation factor subunits. J Biol Chem 281, 176-186 (2006).
4. M. B. Shine et al., Phased small RNA-mediated systemic signaling in plants. Sci Adv 8, eabm8791 (2022).
Keywords: Systemic Acquired Resistance, alternative polyadenylation