In nature, parental responses to environmental stresses can be inherited by their offspring, defending them against the same challenges.1 The nematode Caenorhabditis elegans is an ideal model organism for studying this process due to its short generation time and large brood size.2 In its natural habitat, C. elegans encounters various bacterial pathogens, some of which can have detrimental effects.2 To ensure survival and reproduction, C. elegans has evolved a sophisticated set of pathogen defences that are transmitted to subsequent generations, safeguarding its offspring from similar threats.
Certain Pseudomonas species are pathogenic to C. elegans. Exposure to Pseudomonas aeruginosa (PA14) or Pseudomonas vranovensis can kill worms within hours or days.3,4 When parental worms are exposed to PA14 or P. vranovensis, their offspring exhibit avoidance behavior toward these bacteria, and this pathogenic avoidance is inherited for multiple generations.3,4,5 These heritable processes depend on the PRG-1/piRNA pathway and transgenerational epigenetic inheritance pathways, which are mediated by heritable histone modifications and small RNAs.4,6 Interestingly, small RNAs from pathogenic bacteria can induce heritable adaptations to infection.7 Apart from small RNAs, bacterial toxins and cues also drive protective responses in worms.1
In a recent study, Pender et al.8 investigated the roles of bacterial cues in heritable resistance to infection by exposing worms to pathogen-derived volatiles. Consistent with a previous finding showing that direct parental exposure to P. vranovensis enhances offspring survival when encountering the same bacterium,3 progeny from P. vranovensis volatile-exposed parents also exhibited enhanced survival. This suggests that exposure to P. vranovensis volatiles initiates a heritable protective response.
When parental worms were exposed to PA14 or P. vranovensis volatiles, the expression of the cyanoalanine synthase CYSL-2 increased in both parents and offspring, indicating that CYSL-2 plays an essential role in intergenerational adaptation to PA14 and P. vranovensis infections. Additionally, the expression of glutathione S-transferase (GST)-4 also increased following exposure to PA14 or P. vranovensis volatiles. The authors utilized YFP and GFP reporters driven by the promoters of cysl-2 and gst-4 (cysl-2p::venus and gst-4p::gfp) to assess transcriptional levels.
PA14 and P. vranovensis produce cyanide, which increases the expression of cysl-2p::venus and gst-4p::gfp, suggesting that cyanide drives the transcriptional changes induced by volatile exposure. Upon sensing cyanide, CYSL-2 initiates a transcriptional response and detoxifies cyanide through its β-cyanoalanine synthase activity. This transcriptional response can be intergenerationally inherited from parental worms to their offspring. Interestingly, CYSL-2 functions in parents, not the progeny, to regulate heritable transcriptional responses and protect offspring. Cyanide detoxification by CYSL-2 generates two byproducts, β-cyanoalanine and hydrogen sulfide,9 both capable of inducing transcriptional responses, as evidenced by increased cysl-2p::venus and gst-4p::gfp expression in worms upon exposure. However, parental CYSL-2 mediates intergenerational signaling and protection specifically only through β-cyanoalanine, not hydrogen sulfide.
Through RNA interference screening, MDT-15, a nuclear-localized subunit of the Mediator transcriptional regulatory complex, was identified as essential for heritable adaptation to P. vranovensis. Loss of MDT-15 in offspring, but not parents, disrupts heritable transcriptional regulation and protection, suggesting that MDT-15 functions in progeny to mediate intergenerational protection against P. vranovensis. Additionally, the MDT-15 interactor SKN-1, a homolog of Nrf2, which plays a critical role in driving detoxification and immune responses,10 is also essential for the intergenerational protective response.
In summary, parental worms sense and detoxify cyanide, a toxin derived from pathogenic bacteria, through the cyanoalanine synthase CYSL-2, to protect their offspring from the same pathogen via β-cyanoalanine signal. While CYSL-2 functions in parents, transcriptional regulators MDT-15 and SKN-1 act in offspring, working together to drive an intergenerational protective response (Fig. 1). This study highlights a novel mechanism of intergenerational protection against natural pathogens, utilizing a detoxification intermediate rather than previously reported epigenetic mechanisms, such as histone modifications or non-coding RNAs,4,5,6,7 to transmit information from parents to progeny.
Parental C. elegans is exposed to volatiles from PA14 or P. vranovensis. In the parental generation, the cyanoalanine synthase CYSL-2 senses cyanide in the volatiles and detoxifies it into β-cyanoalanine, which acts as an intergenerational signal. In the progeny generation, MDT-15 and the transcription factor SKN-1 drive transcriptional regulation, providing protection against the same bacterial pathogen.
