Identification of Specific Fragments of HpaG_Xooc, a Harpin from Xanthomonas oryzae pv. oryzicola, that Induce Disease Resistance and Enhance Growth in Plants

Abstract

Harpin proteins from gram-negative plant-pathogenic bacteria can stimulate hypersensitive cell death (HCD) and pathogen defense as well as enhance growth in plants. Two of these diverse activities clearly are beneficial and may depend on particular functional regions of the proteins. Identification of beneficial and deleterious regions might facilitate the beneficial use of harpin-related proteins on crops without causing negative effects like cell death. Here, we report the identification and testing of nine functional fragments of HpaG(Xooc), a 137-amino-acid harpin protein from Xanthomonas oryzae pv. oryzicola, the pathogen that causes bacterial leaf streak of rice. Polymerase chain reaction-based mutagenesis generated nine proteinaceous fragments of HpaG(Xooc); these caused different responses following their application to Nicotiana tabacum (tobacco) and Oryza sativa (rice). Fragment HpaG62-137, which spans the indicated amino acid residues of the HpaG, induced more intense HCD; in contrast, HpaG10-42 did not cause evident cell death in tobacco. However, both fragments stimulated stronger defense responses and enhanced more growth in rice than the full-length parent protein, HpaG(Xooc). Of the nine fragments, the parent protein and one deletion mutant of HpaG(Xooc) tested, HpaG10-42, stimulated higher levels of rice growth and resulted in greater levels of resistance to X. oryzae pv. oryzae and Magnaporthe grisea. These pathogens cause bacterial leaf blight and rice blast, respectively, the two most important diseases of rice world-wide. HpaG10-42 was more active than HpaG(Xooc) in inducing expression of several genes that regulate rice defense and growth processes and activating certain signaling pathways, which may explain the greater beneficial effects observed from treatment with that fragment. Overall, our results suggest that HpaG10-42 holds promise for practical agricultural use to induce disease resistance and enhance growth of rice.

Root Growth of Arabidopsis thaliana Is Regulated by Ethylene and Abscisic Acid Signaling Interaction in Response to HrpNEa, a Bacterial Protein of Harpin Group

“…The application of harpins to plants causes multiple effects by stimulating several plant hormones (Chen et al 2008a), including ABA and ethylene (Dong et al 2004(Dong et al , 2005Zhang et al 2007). These hormones often interact to regulate plant defenses towards multiple challenges (Bostock 2005), but there are no reports on the coordinate responses to pleiotropic biotic elicitors, such as harpins.…”

Plant Aquaporin AtPIP1;4 Links Apoplastic H2O2 Induction to Disease Immunity Pathways

“…In addition to AtPIP1;4, immunity-related genes also were analyzed by qRT-PCR. All RT-qPCR analyses were carried out using the SuperScript II RNase HˉReverse Transcriptase Kit (Invitrogen) according to the manufacturer's guide book, and the constitutively expressed ACTIN2 or EF1a gene was used as a reference (Chen et al, 2008). All reactions were performed in triplicate with nulltemplate (complementary DNA-absent) controls.…”

Stimulateurs des défenses naturelles des plantes : une nouvelle stratégie phytosanitaire dans un contexte d’écoproduction durable.

“…Ainsi, la caractérisation récente de neuf régions fonctionnelles sur la harpine de Xanthomonas oryzae pv. oryzicola a permis de constater que chacune d'entre elles exerçait une action différente sur le riz et le tabac (Chen et al 2008). Alors que certaines régions induisent spécifiquement une mort cellulaire, d'autres régions, comme la HpaG10-42, stimulent l'établissement d'une résistance généralisée (de type RSA) en plus de promouvoir la croissance des plantes traitées (Chen et al 2008 Gindro et al (2007) ont conclu que les extraits de graines de fenugrec étaient moins efficaces que des extraits de rhubarbe ou de bourdaine.…”

“…oryzicola a permis de constater que chacune d'entre elles exerçait une action différente sur le riz et le tabac (Chen et al 2008). Alors que certaines régions induisent spécifiquement une mort cellulaire, d'autres régions, comme la HpaG10-42, stimulent l'établissement d'une résistance généralisée (de type RSA) en plus de promouvoir la croissance des plantes traitées (Chen et al 2008 Gindro et al (2007) ont conclu que les extraits de graines de fenugrec étaient moins efficaces que des extraits de rhubarbe ou de bourdaine. Il apparaît ainsi qu'un traitement par pulvérisation du feuillage n'induit que faiblement la synthèse de phytoalexines, ne stimule pas la formation de callose aux sites de pénétration de l'agent pathogène (comme le fait le BABA, par exemple) et ne ralentit que de 40 % la sporulation du champignon.…”