A mutation in the FZL gene of Arabidopsis causing alteration in chloroplast morphology results in a lesion mimic phenotype

Abstract

Lesion mimic mutants (LMMs) are a class of mutants in which hypersensitive cell death and defence responses are constitutively activated in the absence of pathogen attack. Various signalling molecules, such as salicylic acid (SA), reactive oxygen species (ROS), nitric oxide (NO), Ca2+, ethylene, and jasmonate, are involved in the regulation of multiple pathways controlling hypersensitive response (HR) activation, and LMMs are considered useful tools to understand the role played by the key elements of the HR cell death signalling cascade. Here the characterization of an Arabidopsis LMM lacking the function of the FZL gene is reported. This gene encodes a membrane-remodelling GTPase playing an essential role in the determination of thylakoid and chloroplast morphology. The mutant displayed alteration in chloroplast number, size, and shape, and the typical characteristics of an LMM, namely development of chlorotic lesions on rosette leaves and constitutive expression of genetic and biochemical markers associated with defence responses. The chloroplasts are a major source of ROS, and the characterization of this mutant suggests that their accumulation, triggered by damage to the chloroplast membranes, is a signal sufficient to start the HR signalling cascade, thus confirming the central role of the chloroplast in HR activation.

Programmed cell death in plants: A chloroplastic connection

“…20 A recent report suggests that loss of function of FZl gene that encodes a membrane GTPase involved in the determination of thylakoid and chloroplast morphology, in lesion mimic mutant of Arabidopsis is involved in ROS accumulation triggered by damage to the chloroplast membranes, is a signal sufficient to start the HR signaling cascade. 21 Phenylalanine ammonia lyase (PAL) mediated salicylic acid (SA) accumulation has been suggested to be involved in Fumonisin B1 triggered light dependent generation of H 2 O 2 that induces degradation of chloroplast proteins and HR induction in Arabidopsis. 13,19 Chlorophyll break down leading to yellowing of leaves is one of the signatures of senescence that is believed to be a type of PCD.…”

Reactive Oxygen Species and Photosynthesis

“…LSD1 function is necessary for optimum catalase activity and thus determines the efficiency of photorespiration in protection of plants from overreduction of electron transport chain (see Section 1.5.1.7) (Mateo et al, 2004). An Arabidopsis mutant with hypersensitive cell death and constitutively activated defense responses has been found lacking the function of the FZL gene (Landoni et al, 2013). This gene encodes a membrane-remodeling GTPase with an essential role in the determination of thylakoid and chloroplast morphology.…”

“…This gene encodes a membrane-remodeling GTPase with an essential role in the determination of thylakoid and chloroplast morphology. Since the chloroplasts are a major source of ROS, the characterization of this mutant suggests that ROS accumulation, triggered by damage to the chloroplast membranes, is a signal for starting the defense signaling cascade (Landoni et al, 2013).…”

Genetic Mapping and Characterization of Lethal Necrotic Mutants in Rice (<i>Oryza sativa</i> L.)

“…Under stress, ROS production exceeds the cells' scavenging capacity, and the ROS radicals induce necrotic lesions and alter the expression of certain genes in many signaling pathways, eventually leading to accelerated cell death [23] [24]. In maize, Arabidopsis, and rice [25] [26] [27] [28], the accumulation of ROS in particular, H 2 O 2 and the presence of dead cells are studied as biochemical markers constitutively expressed in LMMs [29]. They are commonly monitored by staining using histochemical dyes: 3',3'-diaminobenzidine (DAB) and trypan blue, respectively [29] [30].…”

“…In maize, Arabidopsis, and rice [25] [26] [27] [28], the accumulation of ROS in particular, H 2 O 2 and the presence of dead cells are studied as biochemical markers constitutively expressed in LMMs [29]. They are commonly monitored by staining using histochemical dyes: 3',3'-diaminobenzidine (DAB) and trypan blue, respectively [29] [30]. Although H 2 O 2 is known to cause cell death leading to necrotic lesions in many plants [31], little is known about ROS-induced necrotic lethality.…”