Plant Signals Anticipate the Induction of the Type III Secretion System in Pseudomonas syringae pv. actinidiae , Facilitating Efficient Temperature-Dependent Effector Translocation

Abstract

Plant diseases—their occurrence and severity—result from the impact of three factors: the host, the pathogen, and the environmental conditions, interconnected in the disease triangle. Time was further included as a fourth factor accounting for plant disease, leading to a more realistic three-dimensional disease pyramid to represent the evolution of disease over time.

Some like it hot: efficiency of the type III secretion system and activation of plant defenses have multiple thermosensitive behaviors in thePseudomonas syringaecomplex

“…Regarding P. syringae pv. actinidiae , our results confirmed a low-temperature dependency for T3SS efficiency (Puttilli et al ., 2022), which is entirely in line with the environmental conditions – in late winter or early spring – under which P. syringae pv. actinidiae is reported to cause disease or damage in the kiwifruit orchards (Kim et al ., 2017; Donati et al ., 2020).…”

“…glycinea could be involved in the regulation of T3SS-related gene expression in response to temperature (Ullrich et al ., 1995). Alternatively, if evidence hints that gene expression is not directly modified by temperature (Puttilli et al ., 2022), thermoregulation might act later in the transcription/translation chain, during T3SS assembly, or on translocation efficiency. In addition, the study of potential differences in membrane fluidity between strains is promising.…”

“…For each technical replicate, the conductivity value from the first measure was subtracted to values measured at each successive time points for normalization (Puttilli et al ., 2022). For each strain-temperature modality within each replicated experiment, conductivity was calculated as the average of the values of the three technical replicates for each time point, and ion-leakage curves over time were established accordingly.…”

“…On the other hand, for P. syringae pv. actinidiae strains, it was shown that there was no difference in hrpA1 promoter activity in vitro across a temperature range of 18-28°C, nonetheless, substantial differences were evident at a functional level, demonstrating a low-temperature dependency for T3SS efficiency for these strains (Puttilli et al ., 2022). However, the complete implications of warm temperatures on P. syringae virulence in plants remain poorly understood (Li et al ., 2006; Hockett et al ., 2013).…”

Effects of T3SS-positive Pseudomonas isolates on sugar beet growth stimulation and pathogen resistance

“…Interestingly, our results showed that 6 out of 10 isolates exhibited signi cant upregulation of T3SS expression in the presence of sugar beet extract, highlighting the speci city of this system to the sugar beet host and suggesting a specialised mechanism for the delivery of T3Es to this particular plant species. This observation is consistent with the existing literature on pathogens in which host-speci c signalling triggers T3SS expression (Puttilli et al, 2022). Contrary to expectations, the addition of sugar beet extract led to a down-regulation of T3SS expression in certain isolates, including the aforementioned P. corrugata MRh80.…”