Chitin synthase is involved in vegetative growth, asexual reproduction and pathogenesis of Phytophthora capsici and Phytophthora sojae

Abstract

Summary Chitin is a structural and functional component of the fungal cell wall and also serves as a pathogen‐associated molecular pattern (PAMP) that triggers the innate immune responses of host plants. However, no or very little chitin is found in the fungus‐like oomycetes. In Phytophthora spp., the presence of chitin has not been demonstrated so far, although putative chitin synthase (CHS) genes, which encode the enzymes that synthesize chitin, are present in their genomes. Here, we revealed that chitin is present in the zoospores and released sporangia of Phytophthora, and this is most consistent with the transcriptional pattern of PcCHS in Phytophthora capsici and PsCHS1 in Phytophthora sojae. Disruption of the CHS genes indicated that PcCHS and PsCHS1, but not PsCHS2 (which exhibited very weak transcription), have similar functions involved in mycelial growth, sporangial production, zoospore release and the pathogenesis of P. capsici and P. sojae. We also suggest that chitin in the zoospores of P. capsici can act as a PAMP that is recognized by the chitin receptors AtLYK5 or AtCERK1 of Arabidopsis. These results provide new insights into the biological significance of chitin and CHSs in Phytophthora and help with the identification of potential targets for disease control.

Identification and Characterization of the Chitin Synthase Genes From the Fish Pathogen Saprolegnia parasitica

“…Nonetheless, the activity of the corresponding Chs product seems to be required for vegetative growth as the presence of NZ in the culture medium results in strong growth inhibition (Hinkel and Ospina-Giraldo, 2017) and tip bursting (Klinter et al, 2019). This was confirmed in recent work in other Phytophthora species where CHS proteins have been shown to be involved in vegetative growth, asexual reproduction, and pathogenesis (Cheng et al, 2019). Although the function of the P. infestans Chs gene remains elusive, its high expression during plant infection suggests that it has a specific role in pathogenesis (Hinkel and Ospina-Giraldo, 2017).…”

The transcriptional reprograming and functional identification of WRKY family members in pepper’s response to Phytophthora capsici infection

“…The seeds of P. capsici-resistant pepper landrace line 'Criollo de Morelos 334' (CM334) and susceptible cultivar 'Early Calwonder 01' (EC01) were sown in a soil mix [peat moss: perlite, 2:1 (v/v)] in plastic pots, and were placed in a growth room under a condition of 25°C, 60-70 mmol photons m − 2 s − 1 , a relative humidity of 70%, and a 16-h light/8-h dark photoperiod [29]. A highly virulent P. capsici stain JX1 was isolated by our laboratory and cultured as described previously [42]. Briefly, the P. capsici stain was cultured on 10% (v/v) V8 agar medium, and then transferred to 10% (v/v) V8 liquid medium for 3 days at 25°C in the dark.…”

“…Briefly, the P. capsici stain was cultured on 10% (v/v) V8 agar medium, and then transferred to 10% (v/v) V8 liquid medium for 3 days at 25°C in the dark. The mycelia of P. capsici were washed intermittently with sterilized H 2 O for three times to induce zoospore release [42].…”

“…Total RNA was extracted from P. capsici-infected pepper tissues at the indicated time points as described previously [42]. In brief, total RNA was extracted by a Pure-Link RNA mini kit (Invitrogen, Carlsbad, CA, USA) and treated with RNase-free DNase I (Takara Bio, Kusatsu, Japan).…”

“…For infection assays, the third and fourth detached leaves from the top of each TRV treated pepper plant were inoculated with the highly virulent P. capsici stain JX1 zoospores, respectively [42]. To distinguish the disease phenotypes among different VIGS plants, especially for the susceptible pepper line EC01, each detached leaf was inoculated with~100 P. capsici zoospores (a relative low concentration) under low disease-pressure conditions.…”