Haemoglobin modulates salicylate and jasmonate/ethylene-mediated resistance mechanisms against pathogens

Abstract

Nitric oxide (NO) plays a role in defence against hemibiotrophic pathogens mediated by salicylate (SA) and also necrotrophic pathogens influenced by jasmonate/ethylene (JA/Et). This study examined how NO-oxidizing haemoglobins (Hb) encoded by GLB1, GLB2, and GLB3 in Arabidopsis could influence both defence pathways. The impact of Hb on responses to the hemibiotrophic Pseudomonas syringae pathovar tomato (Pst) AvrRpm1 and the necrotrophic Botrytis cinerea were investigated using glb1, glb2, and glb3 mutant lines and also CaMV 35S GLB1 and GLB2 overexpression lines. In glb1, but not glb2 and glb3, increased resistance was observed to both pathogens but was compromised in the 35S-GLB1. A quantum cascade laser-based sensor measured elevated NO production in glb1 infected with Pst AvrRpm1 and B. cinerea, which was reduced in 35S-GLB1 compared to Col-0. SA accumulation was increased in glb1 and reduced in 35S-GLB1 compared to controls following attack by Pst AvrRpm1. Similarly, JA and Et levels were increased in glb1 but decreased in 35S-GLB1 in response to attack by B. cinerea. Quantitative PCR assays indicated reduced GLB1 expression during challenge with either pathogen, thus this may elevate NO concentration and promote a wide-ranging defence against pathogens.

Scavenging Iron: A Novel Mechanism of Plant Immunity Activation by Microbial Siderophores

“…2). We selected genes involved in two types of functions: WRKY46 (Hu et al, 2012), WRKY70 (Li et al, 2006), and ARABIDOPSIS HEMOGLOBIN1 (AHB1; Mur et al, 2012) involved in plant defense and signaling, and bHLH38 (Yuan et al, 2008;Sivitz et al, 2012), bHLH100, and bHLH101 (Sivitz et al, 2012) involved in iron homeostasis and signaling. In roots, we monitored the expression of a gene involved in nicotianamine biosynthesis: NICOTIANAMINE SYNTHASE1 (NAS1; Klatte et al, 2009 (Curie et al, 2009).…”

Hemoglobin Control of Cell Survival/Death Decision Regulates in Vitro Plant Embryogenesis

“…In plants, Hbs are regulated by many abiotic and biotic stress responses characterized by the manifestation of PCD (Hill, 2012). Independent studies show that overexpression of Hbs reduces aerenchyma formation (Dordas et al, 2003) and represses cell death after pathogen infection (Mur et al, 2012). A key role played by plant Hbs during development and stress responses is to scavenge NO through an NADH-dependent dioxygenase (Igamberdiev et al, 2014).…”

Hemoglobin regulation of plant embryogenesis and plant pathogen interaction

“…33 Altering endogenous Hb1 in transgenic Arabidopsis, affected the disease response toward different pathogens including the strong necrotrophic fungus Botrytis cinerea. 34 Interestingly increased disease symptoms were observed in both up and downregulating lines, compared with controls. The increase in symptoms due to tissue, this model opens interesting avenues for dissecting HBs signaling in plants.…”

“…22 Increasing NO levels in Arabidopsis leaves by suppressing expression of Hb1 also resulted in JA accumulation. 25 Apparently contrasting responses were observed in tomato plants, where NO application was found to be inhibitory toward the JA mediated wound responses. 26 Many of the responses due to NO downregulation of Hb1 was accompanied with an increase in NO and H 2 O 2 , followed by a rise in JA.…”