Ethylene Signaling Pathway and MAPK Cascades Are Required for AAL Toxin–Induced Programmed Cell Death

Abstract

Programmed cell death (PCD), known as hypersensitive response cell death, has an important role in plant defense response. The signaling pathway of PCD remains unknown. We employed AAL toxin and Nicotiana umbratica to analysis plant PCD. AAL toxin is a pathogenicity factor of the necrotrophic pathogen Alternaria alternata f. sp. lycopersici. N. umbratica is sensitive to AAL toxin, susceptible to pathogens, and effective in Tobacco rattle virus-based virus-induced gene silencing (VIGS). VIGS analyses indicated that AAL toxin-triggered cell death (ACD) is dependent upon the mitogen-activated protein (MAP) kinase kinase MEK2, which is upstream of both salicylic acid-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK) responsible for ethylene (ET) synthesis. ET treatment of MEK2-silenced N. umbratica re-established ACD. In SIPK- and WIPK-silenced N. umbratica, ACD was compromised and ET accumulation was not observed. However, in contrast to the case of MEK2-silenced plants, ET treatment did not induce cell death in SIPK- and WIPK-silenced plants. This work showed that ET-dependent pathway and MAP kinase cascades are required in ACD. Our results suggested that MEK2-SIPK/WIPK cascades have roles in ET biosynthesis; however, SIPK and WIPK have other roles in ET signaling or another pathway leading to cell death by AAL toxin.

Ethylene: traffic controller on hormonal crossroads to defense

“…Moreover, SIPK-and WOUND INDUCED PROTEIN KINASE-silenced Nicotiana umbratica plants showed disrupted ET accumulation and compromised necrosis upon application of the pathogen-derived Alternaria alternata sp. lycopersici toxin (Mase et al, 2012). Taken together, these results highlight the importance of MAPK signaling cascades in the regulation of ET signaling and its downstream defense responses.…”

“…For example, during infection of Arabidopsis by the necrotrophic pathogen Botrytis cinerea, MITOGEN-ACTIVATED PROTEIN KINASE3 (MPK3) and MPK6 phosphorylate the ET biosynthesis proteins 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID (ACC) SYNTHASE2 (ACS2) and ACS6, resulting in rapid ET production (Han et al, 2010). Additionally, silencing SALICYLIC ACID-INDUCED PROTEIN KINASE (SIPK), encoding the N. attenuata ortholog of Arabidopsis MPK6, abolished insect-induced ET accumulation in N. attenuata (Wu et al, 2007;Mase et al, 2012). Moreover, SIPK-and WOUND INDUCED PROTEIN KINASE-silenced Nicotiana umbratica plants showed disrupted ET accumulation and compromised necrosis upon application of the pathogen-derived Alternaria alternata sp.…”

Ethylene signalling is essential for the resistance of Nicotiana attenuata against Alternaria alternata and phytoalexin scopoletin biosynthesis

“…lycopersici causes diseases on tomato by producing AAL toxin (Akamatsu et al, 1997). Ethylene signalling was induced by the infection of this fungus or treatments of AAL toxin, and conferred host susceptibility rather than resistance to this pathogen, probably by promotion of AAL toxin-induced cell death (Zhang et al, 2011;Mase et al, 2012;Jia et al, 2013). However, this is not the case in the N. attenuata-A.…”

Managing potato wart: a review of present research status and future perspective

“…Next generation sequencing approaches on appropriate genetic materials combined with bioinformatics for sequence analysis are new possibilities to study this pathosystem at the molecular level. Most plant responses to biotic stress involve programmed cell death (PCD) mediated by signal transduction pathways (Turner et al 2002; Suzuki 2002; Townley et al 2005; Mase et al 2012; Gruska 2013). Dissecting the signal transduction pathways controlling wart disease in potato represents a promising direction.…”