Crops of the future: building a climate-resilient plant immune system

Abstract

A grand challenge facing plant scientists today is to find innovative solutions to increase global crop production in the context of an increasingly warming climate. A major roadblock to global food sufficiency is persistent loss of crops to plant diseases and insect infestations. The United Nations has declared 2020 as the International Year of Plant Health. For historical reasons, molecular studies of plant-biotic interactions in the past several decades have not paid enough attention to how variable climate conditions affect plant-biotic interactions. Here, we highlight a few recent studies that begin to reveal how major climatic drivers impact the plant immune system, particularly secondary messenger and defense hormone signaling, and discuss possible approaches toward engineering climate-resilient plant immunity as part of an ongoing global effort to design 'dream' crops of the future.

Figure 1.. A simplified diagram depicting the impact of elevated temperature on PTI, ETI, SA and JA immune signaling modules.

Plants can recognize pathogens through (i) cell surface-localized pattern-recognition receptors (PRRs), which perceive conserved microbial patterns, such as bacterial flagellin, and (ii) intracellularly-localized nucleotide-binding, leucine-rich repeat proteins (NLRs), which recognize effector proteins secreted into the plant cell during infection, leading to pattern-triggered immunity (PTI) and effector-triggered immunity (ETI), respectively. Activation of PTI and ETI evokes an increase in secondary messengers, such as reactive oxygen species (ROS) and calcium ions (shown for PTI), and production of SA and subsequent signaling through NPR receptors and TGA transcription factors. As discussed in this paper, elevated temperature (indicated by a thermometer with an upward arrow) has been shown to downregulate ETI, PTI and SA production and signaling (indicated by blue suppression arrows). In contrast, elevated temperature potentiates wound-induced JA signaling through stabilization of the JA receptor coronatine-insensitive 1 (COI1) protein with increased heat shock protein 90 (HSP90) (indicated by a horizontal red arrow). PAMP: Pathogen-associated molecular pattern; ICS1: Isochorismate synthase 1; MAPK: Mitogen-activated protein kinase; SA: Salicylic acid; JA: Jasmonic acid; NPR: Nonexpressor of PR Genes. Created with BioRender.com.

Figure 2.. Building a climate-resilient plant immune system.

Molecular breeding utilizing pangenomic and biotechnological methods, such as CRISPR/Cas9 and uORF-mediated translational control, will allow researchers to develop crops with climate-resilient PTI, ETI, SA and JA signaling modules and other immune responses (not shown). Created with BioRender.com.