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Abstract
Plants have evolved an array of defenses against pathogens. However, mounting a defense
response frequently comes with the cost of a reduction in growth and reproduction,
carrying critical implications for natural and agricultural populations. This review
focuses on how costs are generated and whether and how they can be mitigated. Most
well-characterized growth-defense trade-offs stem from antagonistic crosstalk among
hormones rather than an identified metabolic expenditure. A primary way plants mitigate
such costs is through restricted expression of resistance; this can be achieved through
inducible expression of defense genes or by the concentration of defense to particular
times or tissues. Defense pathways can be primed for more effective induction, and
primed states can be transmitted to offspring. We examine the resistance (R) genes
as a case study of how the toll of defense can be generated and ameliorated. The fine-scale
regulation of R genes is critical to alleviate the burden of their expression, and
the genomic organization of R genes into coregulatory modules reduces costs. Plants
can also recruit protection from other species. Exciting new evidence indicates that
a plant's genotype influences the microbiome composition, lending credence to the
hypothesis that plants shape their microbiome to enhance defense.