Abstract
Calcium signals are crucial for the activation and coordination of signaling cascades leading to the establishment of plant defense mechanisms. Here, we studied the contribution of CML8, an Arabidopsis calmodulin-like protein in response to Ralstonia solanacearum and to pathogens with different lifestyles, such as Xanthomonas campestris pv. campestris and Phytophtora capsici. We used pathogenic infection assays, gene expression, RNA-seq approaches, and comparative analysis of public data on CML8 knockdown and overexpressing Arabidopsis lines to demonstrate that CML8 contributes to defense mechanisms against pathogenic bacteria and oomycetes. CML8 gene expression is finely regulated at the root level and manipulated during infection with Ralstonia, and CML8 overexpression confers better plant tolerance. To understand the processes controlled by CML8, genes differentially expressed at the root level in the first hours of infection have been identified. Overexpression of CML8 also confers better tolerance against Xanthomonas and Phytophtora, and most of the genes differentially expressed in response to Ralstonia are differentially expressed in these different pathosystems. Collectively, CML8 acts as a positive regulator against Ralstonia solanaceraum and against other vascular or root pathogens, suggesting that CML8 is a multifunctional protein that regulates common downstream processes involved in the defense response of plants to several pathogens.
Highlights
In their environment, plants have to face many constraints in order to carry out their development and reproduction cycles
As CML8 was shown to act as a positive regulator of plant defense responses against Pst [26], and considering that CML8 expression was restricted to lateral roots (LRs) initiations that are considered an entry point for many plant soil pathogens, we investigated the contribution of CML8 in response to the soilborne bacterium Ralstonia solanacearum (Rs) [33]
Eight and two differentially expressed genes (DEGs) were identified in knockdown amiRNA 2.3.2 (KD) and OECML8 2.3 (OE2), respectively, and none of these genes were present in the list of 151 DEGs, suggesting that CML8 may act as a sensor tightly regulated by the plant to rapidly cope with external stimuli such as interaction with pathogens at the root level during development
Summary
Plants have to face many constraints in order to carry out their development and reproduction cycles These stressful conditions induce on the plant varied responses depending on the biotic and abiotic stimuli detected [1,2]. Plant defense mechanisms against a limited number of pathogens have been extensively studied They depend on physical responses that involve specific structures, such as the plant cell wall or the presence of the cuticle, and two layers of immune responses. To overcome PTI, some pathogens produce effectors that interfere with host defense responses Such effectors can be recognized by intracellular resistance proteins which activate the second layer of plant defense, called the effector-triggered immunity (ETI) [6], which often restricts further spread of the pathogen through a localized programmed cell death [7]. The more complex nature of plant immunity is illustrated by the diversity of defense response phenotype observed in natural and field conditions [10,11] and the recent study of the genetic basis of quantitative disease resistance (QDR) suggests that this phenomenon is explained by a polygenic architecture [12,13]
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