title: XA27 depends on an amino-terminal signal-anchor-like sequence to localize to the apoplast for resistance to Xanthomonas oryzae pv oryzae.
abstract: The rice (Oryza sativa) gene Xa27 confers resistance to Xanthomonas oryzae pv oryzae, the causal agent of bacterial blight disease in rice. Sequence analysis of the deduced XA27 protein provides little or no clue to its mode of action, except that a signal-anchor-like sequence is predicted at the amino (N)-terminal region of XA27. As part of an effort to characterize the biochemical function of XA27, we decided to determine its subcellular localization. Initial studies showed that a functional XA27-green fluorescent protein fusion protein accumulated in vascular elements, the host sites where the bacterial blight pathogens multiply. The localization of XA27-green fluorescent protein to the apoplast was verified by detection of the protein on cell walls of leaf sheath and root cells after plasmolysis. Similarly, XA27-FLAG localizes to xylem vessels and cell walls of xylem parenchyma cells, revealed by immunogold electron microscopy. XA27-FLAG could be secreted from electron-dense vesicles in cytoplasm to the apoplast via exocytosis. The signal-anchor-like sequence has an N-terminal positively charged region including a triple arginine motif followed by a hydrophobic region. Deletion of the hydrophobic region or substitution of the triple arginine motif with glycine or lysine residues abolished the localization of the mutated proteins to the cell wall and impaired the plant's resistance to X. oryzae pv oryzae. These results indicate that XA27 depends on the N-terminal signal-anchor-like sequence to localize to the apoplast and that this localization is important for resistance to X. oryzae pv oryzae.
authors.affiliation: Temasek Life Sciences Laboratory, National University of Singapore, Singapore 117604, Republic of Singapore.
authors.forename: Lifang
authors.initials: L
authors.lastname: Wu
authors.forename: Mei Ling
authors.initials: ML
authors.lastname: Goh
authors.forename: Chellamma
authors.initials: C
authors.lastname: Sreekala
authors.forename: Zhongchao
authors.initials: Z
authors.lastname: Yin
mesh_terms: D017343:Genes, Plant; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics* / Q000382:microbiology / Q000648:ultrastructure; D013347:Subcellular Fractions / Q000378:metabolism; D014974:Xanthomonas / Q000472:pathogenicity*
chemical_list: D049452:Green Fluorescent Proteins
references.citation: Science. 2007 Feb 23;315(5815):1098-103
references.pmid: 17185563
references.citation: EMBO J. 2000 Aug 1;19(15):4004-14
references.pmid: 10921881
references.citation: Plant Physiol. 1992 Jul;99(3):1044-50
references.pmid: 16668969
references.citation: Annu Rev Plant Biol. 2003;54:23-61
references.pmid: 14502984
references.citation: Plant Physiol. 1995 Apr;107(4):1333-41
references.pmid: 7770527
references.citation: Plant J. 2000 May;22(4):345-54
references.pmid: 10849351
references.citation: Annu Rev Phytopathol. 2007;45:101-27
references.pmid: 17352660
references.citation: Cell. 2002 May 31;109(5):589-98
references.pmid: 12062102
references.citation: Proc Natl Acad Sci U S A. 2006 Dec 5;103(49):18395-400
references.pmid: 17082309
references.citation: Cell. 2003 Feb 7;112(3):369-77
references.pmid: 12581526
references.citation: Biochim Biophys Acta. 2004 Nov 11;1694(1-3):135-47
references.pmid: 15546663
references.citation: Science. 1995 Dec 15;270(5243):1804-6
references.pmid: 8525370
references.citation: FEBS J. 2006 Nov;273(21):4817-30
references.pmid: 16987314
references.citation: Fungal Genet Biol. 1998 Aug;24(3):285-97
references.pmid: 9756710
references.citation: Mol Plant Microbe Interact. 2001 Dec;14(12):1411-9
references.pmid: 11768536
references.citation: Plant J. 2004 Jan;37(2):301-14
references.pmid: 14690513
references.citation: Nat Protoc. 2007;2(4):953-71
references.pmid: 17446895
references.citation: Mol Membr Biol. 2005 Jan-Apr;22(1-2):113-21
references.pmid: 16092529
references.citation: Biochim Biophys Acta. 1988 Jun 9;947(2):307-33
references.pmid: 3285892
references.citation: Science. 1996 Dec 20;274(5295):2060-3
references.pmid: 8953033
references.citation: Cell. 2000 May 12;101(4):353-63
references.pmid: 10830163
references.citation: Nature. 2005 Jun 23;435(7045):1122-5
references.pmid: 15973413
references.citation: PLoS Biol. 2007 Mar;5(3):e68
references.pmid: 17298188
references.citation: Biochim Biophys Acta. 2004 Nov 11;1694(1-3):181-206
references.pmid: 15546666
references.citation: Plant J. 1999 Apr;18(2):205-14
references.pmid: 10363372
references.citation: Proc Natl Acad Sci U S A. 2003 Jun 24;100(13):8024-9
references.pmid: 12788974
references.citation: Science. 1996 Dec 20;274(5295):2063-5
references.pmid: 8953034
references.citation: Annu Rev Phytopathol. 2005;43:395-436
references.pmid: 16078890
references.citation: Proc Natl Acad Sci U S A. 1998 Dec 22;95(26):15849-54
references.pmid: 9861059
references.citation: Nature. 2001 Jun 14;411(6839):826-33
references.pmid: 11459065
references.citation: Annu Rev Plant Physiol Plant Mol Biol. 1997 Jun;48:575-607
references.pmid: 15012275
references.citation: Theor Appl Genet. 2004 Mar;108(5):800-7
references.pmid: 15118822