Growth-defense tradeoffs in plants: a balancing act to optimize fitness

Abstract

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.

Keywords: PAMP; jasmonate; plant growth.; plant hormone; plant immunity; salicylic acid.

Figure 1

A diagram depicting the concept of growth-defense tradeoffs. Plants use photosynthesis to convert light energy into chemical energy in the form of carbohydrates. These resources are then allocated towards growth or defense, depending on the presence or absence of specific stresses. This process is facilitated by hormone crosstalk and is referred to as the growth–defense tradeoff. BR, brassinosteroid; GA, gibberellin; PTI, pathogen-associated-molecular-pattern-triggered immunity; SA, salicylic acid; JA, jasmonates.

Figure 2

Known Signaling Contributing to Growth–Defense Tradeoffs between PTI-Mediated Defense and Auxin-, Brassinosteroid (BR)-, and Gibberellin (GA)-Mediated Growth. Black arrows and red, blunted lines represent positive and negative regulation, respectively. Double helices with arrows represent global transcriptional reprogramming, and gray lines with dots at both ends indicate protein–protein interactions. Solid lines indicate a known connection between two components, whereas dashed lines indicate unknown connections or missing steps between two components. The solid blue line with an arrow represents expression of TIR1/AFB genes, the transcripts of which are targeted by miR393. FLS2, FLAGELLIN SENSING 2; ROS, reactive oxygen species; WRKY, WRKY DNA-BINDING PROTEIN; miR393, microRNA 393; TIR1, TRANSPORT INHIBITOR RESPONSE 1; AFB, AUXIN SIGNALING F-BOX; AUX/IAA, AUXIN-INDUCIBLE/INDOLE-3-ACETIC ACID INDUCIBLE; ARF, AUXIN RESPONSE FACTOR; BAK1, BRI1-ASSOCIATED RECEPTOR KINASE 1; BRI1, BRASSINOSTEROID INSENSITIVE 1; BSU1, BRI1 SUPPRESSOR 1; BIN2, BRASSINOSTEROID INSENSITIVE 2; BES1, BRI1-EMS-SUPPRESSOR 1; BZR1, BRASSINAZOLE-RESISTANT 1; SLY1, SLEEPY 1; GID1, GA INSENSITIVE DWARF 1A; DELLA, repressor protein; PIF, PHYTOCHROME INTERACTING FACTOR.

Figure 3

Known Signaling Contributing to Growth–Defense Tradeoffs between Salicylic Acid (SA)-Mediated Defense and Auxin-, Brassinosteroid (BR)-, and Gibberellin (GA)-Mediated Growth. As in Figure 2, black arrows and red, blunted lines represent positive and negative regulation, respectively. Double helices with arrows represent global transcriptional reprogramming, and solid lines associated with arrows represent expression of TIR1/AFB and GH3.5 genes. Solid lines indicate a known connection between two components, whereas dashed lines indicate unknown connections or missing steps in between two components. NPR1, NONEXPRESSOR OF PR GENES 1; TGA, TGACG SEQUENCE-SPECIFIC BINDING PROTEIN; PR, PATHOGENESIS RELATED; IAA, INDOLE-3-ACETIC ACID; Asp, aspartate; TIR1, TRANSPORT INHIBITOR RESPONSE 1; AFB, AUXIN SIGNALING F-BOX; AUX/IAA, AUXIN-INDUCIBLE/IAA INDUCIBLE; ARF, AUXIN RESPONSE FACTOR.

Figure 4

Known Signaling Contributing to Growth–Defense Tradeoffs between Jasmonate (JA)-Mediated Defense and Auxin-, Brassinosteroid (BR)-, and Gibberellin (GA)-Mediated Growth. As in Figures 2 and 3, black arrows and red, blunted lines represent positive and negative regulation, respectively. Double helices with arrows represent global transcriptional reprogramming, and solid lines with arrows represent expression of JAZ and PLT genes. Solid lines indicate a known connection between two components, whereas dashed lines indicate unknown connections or missing steps in between two components. COI1, CORONATINE INSENSITIVE 1; JAZ, JASMONATE ZIM DOMAIN; MYC, transcription factor; SLY1, SLEEPY 1; GID1, GA INSENSITIVE DWARF 1A; DELLA, repressor protein; PIF, PHYTOCHROME INTERACTING FACTOR; PLT, PLETHORA.