It's a matter of time: the role of transcriptional regulation in the circadian clock-pathogen crosstalk in plants

Abstract

Most living organisms possess an internal timekeeping mechanism known as the circadian clock, which enhances fitness by synchronizing the internal timing of biological processes with diurnal and seasonal environmental changes. In plants, the pace of these biological rhythms relies on oscillations in the expression level of hundreds of genes tightly controlled by a group of core clock regulators and co-regulators that engage in transcriptional and translational feedback loops. In the last decade, the role of several core clock genes in the control of defense responses has been addressed, and a growing amount of evidence demonstrates that circadian regulation is relevant for plant immunity. A reciprocal connection between these pathways was also established following the observation that in Arabidopsis thaliana, as well as in crop species like tomato, plant-pathogen interactions trigger a reconfiguration of the circadian transcriptional network. In this review, we summarize the current knowledge regarding the interaction between the circadian clock and biotic stress responses at the transcriptional level, and discuss the relevance of this crosstalk in the plant-pathogen evolutionary arms race. A better understanding of these processes could aid in the development of genetic tools that improve traditional breeding practices, enhancing tolerance to plant diseases that threaten crop yield and food security all around the world.

Keywords: Circadian clock; biotic stress; plant-pathogen interaction.

Figure 1.

Time course of the circadian transcriptional reconfiguration after pathogen infection. (a) Meta-analysis of the Howard et al. Arabidopsis RNAseq dataset 1, 6 and 12 hours post infection (h.p.i) with Pst DC3000 [76]. At each time point, the differentially expressed genes (DEG) previously categorized as core clock targets in ChIPseq experiments were classified as circadian controlled genes (CCG) or non-circadian controlled genes (non-CCG) as per [66]. (b) Enrichment analysis of DEG along the post-infection time course. The representation factor (RF) was estimated as in [87]. The probability of each overlapping was determined using the hypergeometric test. The color gradient represents adjusted p values and the differences in bubble size correlate with the representation factor. (c) Expression level of the core circadian clock components. For full datasets and analysis refer to Supplementary Table 1