Abstract
Arabidopsis contains 34 genes for glycosylphosphatidylinositol (GPI)-anchored LTPg proteins. A motif analysis has placed these into four groups. With one exception, all are produced with a signal peptide and are most likely attached to the cell membrane via the GPI anchor. Several of the LTPg genes across the four groups are downregulated in syncytia induced by the beet cyst nematode Heterodera schachtii. We have here studied At3g22600 encoding LTPg5, which is the most strongly downregulated LTPg gene. It is mainly expressed in roots, and a promoter::GUS line was used to confirm the downregulation in syncytia and also showed downregulation in galls of the root knot nematode Meloidogyne incognita. In contrast, infection with bacteria (Pseudomonas syringae) and fungi (Botrytis cinerea) led to the induction of the gene in leaves. This diverse regulation of LTPg5 indicated a role in resistance, which we confirmed with overexpression lines and a T-DNA mutant. The overexpression lines were more resistant to both nematode species and to P. syringae and B. cinerea, while a knock-out mutant was more susceptible to H. schachtii and P. syringae. Thus, LTPg5 encoded by At3g22600 is part of the Arabidopsis resistance mechanism against pathogens. LTPg5 has probably no direct antimicrobial activity but could perhaps act by associating with a receptor-like kinase, leading to the induction of defense genes such as PR1.
Highlights
Plants are under constant pressure from various pathogens and pests
We found that LTPg5 (At3g22600) was one of the most strongly downregulated genes in syncytia, indicating that the LTPg5 protein might have an adverse effect on the development of syncytia or the nematode itself [17]
To further study the expression of LTPg5, we generated a promoter::GUS line. The inoculation of this line with H. schachtii confirmed the downregulation of the gene in syncytia (Figure 6A–F) starting at 5 dpi (Figure 6B), and onward up to 15 dpi (Figure 6C–F)
Summary
Plants are under constant pressure from various pathogens and pests. For protection, they produce physical barriers that can be reinforced in response to pathogen attack. The conserved motifs analysis through MEME Suite identified a total of seven different motifs, with motif 1, 2, and 3 found in the majority of the 34 LTPg proteins occurring 34, 27, and 27 times, respectively These motifs correspond to the LTP domain containing six of the eight cysteine residues. Group 2 comprised of LTPg proteins that possessed highly conserved patterns of motifs and exon-introns in the gene sequence. E analysis of syncytia induced by the beet cyst nematode Heterodera schachtii in Arabidopsis roots [17] found that out of 34 GPI-anchor LTP coding genes, 12 genes showed s2ig.4n.iEfixcaprnetslsyiondiAffnearleynstiisaolf LeTxpPrge5ssion in syncytia (Table S2). To further study the expression of LTPg5, we generated a promoter::GUS line The inoculation of this line with H. schachtii confirmed the downregulation of the gene in syncytia (Figure 6A–F) starting at 5 dpi (Figure 6B), and onward up to 15 dpi (Figure 6C–F).
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