Bhavani Natarajan, Harpreet S Kalsi, Prajakta Godbole, Nilam Malankar, Aarthy Thiagarayaselvam, Sundaresha Siddappa, Hirekodathakallu V Thulasiram, Swarup K Chakrabarti, Anjan K Banerjee

J Exp Bot.; 2018 Apr 9;69(8): 2023-2036. doi: 10.1093/jxb/ery025.

Figure: Phytophthora infestans infection in potato

Abstract

To combat pathogen infection, plants employ local defenses in infected sites and elicit systemic acquired resistance (SAR) in distant tissues. MicroRNAs have been shown to play a significant role in local defense, but their association with SAR is unknown. In addition, no such studies of the interaction between potato and Phytophthora infestans have been reported. We investigated the role of miR160 in local and SAR responses to P. infestans infection in potato. Expression analysis revealed induced levels of miR160 in both local and systemic leaves of infected wild-type plants. miR160 overexpression and knockdown plants exhibited increased susceptibility to infection, suggesting that miR160 levels equivalent to those of wild-type plants may be necessary for mounting local defense responses. Additionally, miR160 knockdown lines failed to elicit SAR, and grafting assays indicated that miR160 is required in both local and systemic leaves to trigger SAR. Consistently, SAR-associated signals and genes were dysregulated in miR160 knockdown lines. Furthermore, analysis of the expression of defense and auxin pathway genes and direct regulation of StGH3.6, a mediator of salicylic acid-auxin cross-talk, by the miR160 target StARF10 revealed the involvement of miR160 in antagonistic cross-talk between salicylic acid-mediated defense and auxin-mediated growth pathways. Overall, our study demonstrates that miR160 plays a crucial role in local defense and SAR responses during the interaction between potato and P. infestans.

See https://pubmed.ncbi.nlm.nih.gov/29390146/

Fig. 1.

Expression of miR160 and StARF10 in local and systemic leaves of wild-type potato (Solanum chacoense) upon Phytophthora infestans infection. (A, B) qRT–PCR analysis of miR160 levels in local leaves (A) and systemic leaves (B) at different time points post-infection. (C–F) RLM-RACE-based isolation of miR160 cleavage product of StARF10 (C) and StARF16 (E); partial mRNA sequence of StARF10 (D) and StARF16 (F) aligned with miR160. Numbers denote the fraction of cloned cleavage products that terminated at different positions (denoted by arrows). (G, H) qRT–PCR analysis of StARF10 in local leaves (G) and systemic leaves (H) at different time points post-infection. For miR160 and StARF10 expression analysis, data represent the mean±SE of two biological replicates with three technical replicates each, plotted by normalizing the P. infestans-treated values with mock-treated values for each time point. Asterisks indicate significant differences (P<0.05) between P. infestans-treated and mock-treated samples for the respective time point as analyzed by Student’s t-test.