Abstract
Studies of early stages of cucumber green mottle mosaic virus (CGMMV) disease have been recently focused on plant molecular responses. However, extreme diurnal environmental temperatures, characteristic of global climate changes, could affect plant susceptibility and disease phenotype progression. Our studies of CGMMV disease progression, under simulated extreme temperature waves, have revealed two new disease initiation phenotypes that developed gradually, preceding severe symptom manifestations of post-recovery CGMMV systemic infections. 'Early post-recovery stage' bright yellow islands (BYIs) with defined boundaries amid asymptomatic leaf blades were first emerging followed by 'late post-recovery stage' BYIs with diffused boundaries. A deduced CGMMV disease progression scheme, postulating BYI symptom occurrence time-windows, revealed BYIs in field grown cucumber plants exposed to extreme diurnal temperatures. Profiling ontology of cucumber differentially expressed genes in BYIs vs the associated dark-green surrounding tissues disclosed activation of jasmonic acid (JA) pathway in 'early post-recovery stage' BYIs. JA signaling was inactivated in 'late post-recovery stage' BYIs concomitant with increasing expressions of JA signaling inhibitors and downregulation of JA responsive phenylpropanoid pathway. Our results disclosed a new phenotypic description of CGMMV disease initiation, characteristic of cucumbers grown under extreme environmental temperature fluctuations. The BYI phenotypes could define a time-window for CGMMV disease management applications.
Highlights
Studies of early stages of cucumber green mottle mosaic virus (CGMMV) disease have been recently focused on plant molecular responses
The various high temperature induced molecular mechanisms are sometimes associated with disease symptom recovery; early manifestations of dark green islands (DGIs) that are indicative of inhibition of viral accumulation in areas surrounded by systemic infections; or the opposite effect of overcoming resistance gene induced hypersensitive response followed by initiation of systemic infections[8,9,10]
bright yellow islands (BYIs) phenotypic stages were not observed in systemically infected CGMMV inoculated cucumber plants that were kept at 25 °C ± 2 (Fig. 1a0–c0) and no distinct BYI manifestations were apparent in CGMMV-infected plants grown at a constant temperature of 32 °C ± 2 during a post-recovery disease progression (Supplementary Fig. S2)
Summary
Studies of early stages of cucumber green mottle mosaic virus (CGMMV) disease have been recently focused on plant molecular responses. Our results disclosed a new phenotypic description of CGMMV disease initiation, characteristic of cucumbers grown under extreme environmental temperature fluctuations. The various high temperature induced molecular mechanisms are sometimes associated with disease symptom recovery; early manifestations of dark green islands (DGIs) that are indicative of inhibition of viral accumulation in areas surrounded by systemic infections; or the opposite effect of overcoming resistance gene induced hypersensitive response followed by initiation of systemic infections[8,9,10]. We have analyzed the effect of combined environmental conditions of high temperatures and fluctuating extreme temperature changes on disease progression in CGMMV infected cucumbers. Our findings could define a stage during CGMMV disease symptom progression, showing unique phenotypic characteristics that mark the appropriate time-window for implementation of disease mitigation strategies in a commercial scale
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