FITNESS Acts as a Negative Regulator of Immunity and Influences the Plant Reproductive Output After Pseudomonas syringae Infection.

Diego Alberto Mengarelli,Lara Roldán Tewes,María Inés Zanor,Salma Balazadeh

doi:10.3389/fpls.2021.606791

Abstract

Plants, as sessile organisms, are continuously threatened by multiple factors and therefore their profitable production depends on how they can defend themselves. We have previously reported on the characterization of fitness mutants which are more tolerant to environmental stresses due to the activation of defense mechanisms. Here, we demonstrate that in fitness mutants, which accumulate moderate levels of salicylic acid (SA) and have SA signaling activated, pathogen infection is restricted. Also, we demonstrate that NPR1 is essential in fitness mutants for SA storage and defense activation but not for SA synthesis after Pseudomonas syringae (Pst) infection. Additionally, these mutants do not appear to be metabolically impared, resulting in a higher seed set even after pathogen attack. The FITNESS transcriptional network includes defense-related transcription factors (TFs) such as ANAC072, ORA59, and ERF1 as well as jasmonic acid (JA) related genes including LIPOXYGENASE2 (LOX2), CORONATINE INSENSITIVE1 (COI1), JASMONATE ZIM-domain3 (JAZ3) and JAZ10. Induction of FITNESS expression leads to COI1 downregulation, and to JAZ3 and JAZ10 upregulation. As COI1 is an essential component of the bioactive JA perception apparatus and is required for most JA-signaling processes, elevated FITNESS expression leads to modulated JA-related responses. Taken together, FITNESS plays a crucial role during pathogen attack and allows a cost-efficient way to prevent undesirable developmental effects.

Highlights

Annual crop yield losses due to pathogen attack are a major concern for producers
The mutants accumulated moderate salicylic acid (SA) levels accompanied by an induction of several SA-signaling marker genes, such as NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1), ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1), and PHYTOALEXIN DEFICIENT4 (PAD4)
We showed that the basal SA content in fitness mutants provides the benefit of limiting bacterial pathogen infection

Summary

Introduction

Annual crop yield losses due to pathogen attack are a major concern for producers. chemical control has been increased, the use of synthetic chemicals represents a threat to global food security and agricultural sustainability (Nelson et al, 2017), and many farmers have started to look into more natural ways for food production. Enhancing plant resistance is an alternative way FITNESS Is a Negative Regulator of Immunity to avoid the use of chemicals. Genes that play roles in disease resistance might affect other important traits such as the response to abiotic factors or yield. Some plant transcription factors (TFs) have been described as master regulators of essential aspects – such as development and stress response – using different approaches. FITNESS protein possesses a single CCT (CONSTANS, CONSTANS-like, and TOC1) domain, first described in the protein CONSTANS (Robson et al, 2001). It is included in a family of uncharacterized genes named CCT motif family genes (Cockram et al, 2012). There are some examples of CCT members involved in biotic stresses, like ZmCCT10, which is responsive to Gibberella stalk rot resistance in maize (Zea mays; Wang et al, 2017), and OsCOL9, identified as an early response gene in rice (Oryza sativa) after Magnaporthe oryzae infection (Liu et al, 2016)

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