Growth-defense tradeoffs are thought to occur in plants due to resource restrictions, which demand prioritization towards either growth or defense, depending on external and internal factors. These tradeoffs have profound implications in agriculture and natural ecosystems, as both processes are vital for plant survival, reproduction, and, ultimately, plant fitness. While many of the molecular mechanisms underlying growth and defense tradeoffs remain to be elucidated, hormone crosstalk has emerged as a major player in regulating tradeoffs needed to achieve a balance. In this review, we cover recent advances in understanding growth-defense tradeoffs in plants as well as what is known regarding the underlying molecular mechanisms. Specifically, we address evidence supporting the growth-defense tradeoff concept, as well as known interactions between defense signaling and growth signaling. Understanding the molecular basis of these tradeoffs in plants should provide a foundation for the development of breeding strategies that optimize the growth-defense balance to maximize crop yield to meet rising global food and biofuel demands.

Environmental conditions profoundly affect plant disease development; however, the underlying molecular bases are not well understood. Here we show that elevated temperature significantly increases the susceptibility of Arabidopsis to Pseudomonas syringae pv. tomato (Pst) DC3000 independently of the phyB/PIF thermosensing pathway. Instead, elevated temperature promotes translocation of bacterial effector proteins into plant cells and causes a loss of ICS1-mediated salicylic acid (SA) biosynthesis. Global transcriptome analysis reveals a major temperature-sensitive node of SA signalling, impacting ~60% of benzothiadiazole (BTH)-regulated genes, including ICS1 and the canonical SA marker gene, PR1. Remarkably, BTH can effectively protect Arabidopsis against Pst DC3000 infection at elevated temperature despite the lack of ICS1 and PR1 expression. Our results highlight the broad impact of a major climate condition on the enigmatic molecular interplay between temperature, SA defence and function of a central bacterial virulence system in the context of a widely studied susceptible plant–pathogen interaction.

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We used wild-type UTEX481; SF33, a shortened-filament mutant strain that shows normal complementary chromatic adaptation pigmentation responses; and FdBk14, an RcaE-deficient strain that lacks light-dependent pigmentation responses, to investigate the molecular basis of the photoregulation of cellular morphology in the cyanobacterium Fremyella diplosiphon. Detailed microscopic and biochemical analyses indicate that RcaE is required for the photoregulation of cell and filament morphologies of F. diplosiphon in response to red and green light.

The orange carotenoid protein (OCP) is a structurally and functionally modular photoactive protein involved in cyanobacterial photoprotection. Using phylogenomic analysis, we have revealed two new paralogous OCP families, each distributed among taxonomically diverse cyanobacterial genomes. Based on bioinformatic properties and phylogenetic relationships, we named the new families OCP2 and OCPx to distinguish them from the canonical OCP that has been well characterized in Synechocystis, denoted hereafter as OCP1. We report the first characterization of a carotenoprotein photoprotective system in the chromatically acclimating cyanobacterium Tolypothrix sp. PCC 7601, which encodes both OCP1 and OCP2 as well as the regulatory fluorescence recovery protein (FRP). OCP2 expression could only be detected in cultures grown under high irradiance, surpassing expression levels of OCP1, which appears to be constitutive; under low irradiance, OCP2 expression was only detectable in a Tolypothrix mutant lacking the RcaE photoreceptor required for complementary chromatic acclimation. In vitro studies show that Tolypothrix OCP1 is functionally equivalent to Synechocystis OCP1, including its regulation by Tolypothrix FRP, which we show is structurally similar to the dimeric form of Synechocystis FRP. In contrast, Tolypothrix OCP2 shows both faster photoconversion and faster back-conversion, lack of regulation by the FRP, a different oligomeric state (monomer compared to dimer for OCP1) and lower fluorescence quenching of the phycobilisome. Collectively, these findings support our hypothesis that the OCP2 is relatively primitive. The OCP2 is transcriptionally regulated and may have evolved to respond to distinct photoprotective needs under particular environmental conditions such as high irradiance of a particular light quality, whereas the OCP1 is constitutively expressed and is regulated at the post-translational level by FRP and/or oligomerization.