title: Enhancement of post-transcriptional gene silencing by grafting.
abstract: We showed previously that grafting transmitted silencing occurred when transgenic ACC oxidase 1 (ACO1) overexpressing tomato plants that also produced siRNAs were grafted onto transgenic stocks that already showed strong silencing. The presence of siRNAs in these overexpressing scions may indicate that silencing, though inefficient, may already occur at a low level before grafting. To test if a silencing state with a relatively high level of target mRNA can be shifted towards further more effective silencing, we grafted an ACO1 antisense (AS) line with a high level of antisense ACO1 transgene mRNA and low level of siRNAs to the ACO1 strong silencer stock. The AS mRNA level was reduced dramatically two weeks after grafting. More interestingly, self-grafting of ACO1 overexpressers and AS lines also induced strong silencing in the scions. We suggest that grafting transmitted silencing may involve the switching from an inefficient or weak silencing state to a stronger silencing by a systemic silencing signal, similar to the change of silencing states that sometimes occurs during development. Control experiments using non-transgenic stocks designed to test whether wounding alone is responsible for generating a signal that enhances silencing in transgenic scions gave negative results. We propose that the build-up of silencing signal and/or molecules at both sides of the grafting junction and their sudden release when the phloem is reconnected may be critical to grafting transmitted silencing.
authors.affiliation: Plant Sciences Division; School of Biosciences; University of Nottingham; Sutton Bonington Campus; Loughborough, UK.
authors.forename: Yuanhuai
authors.initials: Y
authors.lastname: Han
authors.forename: Donald
authors.initials: D
authors.lastname: Grierson
references.citation: FEBS Lett. 2006 Dec 11;580(28-29):6579-86
references.pmid: 17113082
references.citation: Mol Genet Genomics. 2002 Jul;267(5):629-35
references.pmid: 12172802
references.citation: Science. 2004 Nov 5;306(5698):1046-8
references.pmid: 15528448
references.citation: Planta. 1983 Mar;157(2):174-9
references.pmid: 24264072
references.citation: EMBO J. 2003 Feb 3;22(3):633-40
references.pmid: 12554663
references.citation: Plant J. 2004 May;38(4):594-602
references.pmid: 15125766
references.citation: Plant Cell. 1994 Oct;6(10):1401-14
references.pmid: 7994174
references.citation: Plant J. 1998 Sep;15(6):737-746
references.pmid: 29368810
references.citation: Planta. 2007 Jan;225(2):365-79
references.pmid: 16924537
references.citation: FEBS Lett. 2004 Apr 9;563(1-3):123-8
references.pmid: 15063735
references.citation: Plant J. 2002 Feb;29(4):509-19
references.pmid: 11846883
references.citation: Proc Natl Acad Sci U S A. 2006 Oct 10;103(41):14994-5001
references.pmid: 17008405
references.citation: EMBO J. 1997 Aug 1;16(15):4738-45
references.pmid: 9303318
references.citation: Plant J. 2000 Jan;21(1):1-8
references.pmid: 10652145
references.citation: Plant J. 2006 Aug;47(3):383-94
references.pmid: 16771840