Duplication of hsp-110 Is Implicated in Differential Success of Globodera Species under Climate Change

Abstract

Managing the emergence and spread of crop pests and pathogens is essential for global food security. Understanding how organisms have adapted to their native climate is key to predicting the impact of climate change. The potato cyst nematodes Globodera pallida and G. rostochiensis are economically important plant pathogens that cause yield losses of up to 50% in potato. The two species have different thermal optima that may relate to differences in the altitude of their regions of origin in the Andes. Here, we demonstrate that juveniles of G. pallida are less able to recover from heat stress than those of G. rostochiensis. Genome-wide analysis revealed that while both Globodera species respond to heat stress by induction of various protective heat-inducible genes, G. pallida experiences heat stress at lower temperatures. We use C. elegans as a model to demonstrate the dependence of the heat stress response on expression of Heat Shock Factor-1 (HSF-1). Moreover, we show that hsp-110 is induced by heat stress in G. rostochiensis, but not in the less thermotolerant G. pallida. Sequence analysis revealed that this gene and its promoter was duplicated in G. rostochiensis and acquired thermoregulatory properties. We show that hsp-110 is required for recovery from acute thermal stress in both C. elegans and in G. rostochiensis. Our findings point towards an underlying molecular mechanism that allows the differential expansion of one species relative to another closely related species under current climate change scenarios. Similar mechanisms may be true of other invertebrate species with pest status.

Fig. 1.

J2 stage of G. rostochiensis have a higher recovery from acute thermal stress than G. pallida. G. rostochiensis J2 stage has a lower rate of quiescence following a 1 h heat stress at 35 °C than G. pallida (P < 0.01) (A). Mean ± SEM, Log-rank (Mantel–Cox) test, n ≥ 5. G. rostochiensis J2 stage has a higher motility rate following a 35 °C heat stress for a duration of 3–6 h than G. pallida (B). Mean ± SEM, unpaired two-tailed Mann–Whitney test, n ≥ 5, *P < 0.05, **P < 0.01, ***P < 0.001.

Fig. 2.

G. pallida has a lower thermal limit than G. rostochiensis. G. pallida has a significantly higher expression of hsp20 genes, kin-20, mnk-1, and ndk-1 during hatch at 20 °C compared with 15 °C (A), unlike G. rostochiensis (B). Expression of other heat inducible genes is not significantly increased by hatch temperature in either species. Mean ± SEM, Kruskal–Wallis test and Dunn’s multiple comparison test, n ≥ 3, *P < 0.05, **P < 0.01, ***P < 0.001.

Fig. 3.

Increased expression of hsp20 genes with culture temperature is hsf-1-dependent in C. elegans. Expression of hsp20 genes in C. elegans is significantly higher during cultivation at 20 °C or 25 °C compared with 15 and 20 °C, respectively (A). Expression of hsp20 genes is significantly reduced under RNAi knockdown of hsf-1 in C. elegans at 25 °C (B and C) and 20 °C (D and E) but not 15 °C (supplementary fig. S2, Supplementary Material online). Expression of hsp-16.2 is also significantly reduced under RNAi knockdown of daf-16 in C. elegans at 25 °C (B and C) and 20 °C (D and E) but not 15 °C (supplementary fig. S2, Supplementary Material online). Mean ± SEM, Kruskal–Wallis test with a Dunn’s multiple comparison test, n ≥ 3, *P < 0.05, **P < 0.01, ***P < 0.001.

Fig. 4.

Hsp-110 was recently duplicated and gained thermoregulation in G. rostochiensis. qPCR analyses reveals that the hsp-110 transcript common to both Globodera species is not heat inducible, whereas the transcript unique to G. rostochiensis is heat inducible (A). Cloning and sequence analyses revealed that hsp-110 and its promoter is duplicated in G. rostochiensis but only one copy is present in G. pallida (B), which is missing the heat shock element (C). Phylogenetic analysis with deduced amino acid sequences from G. rostochiensis, G. pallida, G. ellingtonae, Heterodera sacchari, Rotylenchulus reniformis, Nacobbus aberrans, Meloidogyne hapla, and Bursaphelenchus xylophilus reveals that duplication of hsp-110 occurred relatively recently in the G. rostochiensis lineage. Identification of the heat shock element is indicated by present (Y), absent (N) or not known (?). Mean ± SEM, Kruskal–Wallis test with a Dunn’s multiple comparison test, n ≥ 3, *P < 0.05, **P < 0.01, ***P < 0.001.

Fig. 5.

Expression of hsp-110 is required for recovery from acute heat stress in C. elegans and G. rostochiensis. During RNAi knockdown of hsp-110 recovery from a heat stress of 3–6 h duration was significantly reduced in C. elegans (A) and G. rostochiensis (B) compared with gfp controls. Mean ± SEM, unpaired two-tailed Mann–Whitney test, n ≥ 5, *P < 0.05, **P < 0.01, ***P < 0.001.