Abstract
AbstractDisease development in plants requires a susceptible host, a virulent pathogen, and a favourable environment. Oomycete pathogens cause many important diseases and have evolved sophisticated molecular mechanisms to manipulate their hosts. Day length has been shown to impact plant–oomycete interactions but a need exists for a tractable reference system to understand the mechanistic interplay between light regulation, oomycete pathogen virulence, and plant host immunity. Here we present data demonstrating that light is a critical factor in the interaction between Arabidopsis thaliana and its naturally occurring downy mildew pathogen Hyaloperonospora arabidopsidis (Hpa). We investigated the role of light on spore germination, mycelium development, sporulation, and oospore formation of Hpa, along with defence responses in the host. We observed abundant Hpa sporulation on compatible Arabidopsis under day lengths ranging from 10 to 14 hr. In contrast, exposure to constant light or constant dark suppressed sporulation. Exposure to constant dark suppressed spore germination, mycelial development, and oospore formation, whereas exposure to constant light stimulated these three stages of development. A biomarker of plant immune system activation was induced under both constant light and constant dark. Altogether, these findings demonstrate that Hpa has the molecular mechanisms to perceive and respond to light and that both the host and pathogen responses are influenced by the light regime. Therefore, this pathosystem can be used for investigations to understand the molecular mechanisms through which oomycete pathogens like Hpa perceive and integrate light signals, and how light influences pathogen virulence and host immunity during their interactions.
Highlights
Environmental factors such as light, temperature, and humidity play a significant role in the infection of plants by microbial pathogens and during disease development (Cheng et al, 2019)
Seedlings exposed to constant light (Figure 8b) and constant dark (Figure 8c) for 72 hr showed GUS activity, indicating constant light and dark regimes trigger immunity. These results indicate that induction of immunity under constant light or dark exposure could contribute to the suppression of the sporulation of Hyaloperonospora arabidopsidis (Hpa)
Using the Hpa–Arabidopsis reference system, we showed that light regimes significantly affect several stages of the Hpa disease cycle, including spore germination, mycelial development, oospore formation, and sporulation
Summary
Light is known to have an effect on sporulation of several fungal and oomycete species, and the circadian clock of one fungal phytopathogen has been linked to the pathogen's virulence programme (Hevia et al, 2015). Much recent progress has been made in understanding plant–oomycete interactions through the development of reference plant–oomycete pathosystems that are amenable to genomic, genetic, and molecular approaches (Herlihy et al, 2019) One such pathosystem is the downy mildew pathogen Hyaloperonospora arabidopsidis (Hpa) and its natural host Arabidopsis thaliana (Coates and Beynon, 2010). Elucidating the effect of light on the sporulation and growth of Hpa may give some clue as to whether there is a circadian regulation of its life cycle. We report the effect of different light/dark regimes on the germination, mycelial development, and sporulation of Hpa
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