Not to Be Overlooked: Dipeptides and Their Role in Plant Stress Resilience.

Dipeptides are structurally diverse small molecules with varying modes of biogenesis and function. In plants, dipeptides were historically associated with nitrogen storage and mobilization; however, they are also reported to act as antioxidants, signaling molecules, protein regulators, and modulators of microbial communities. In this review, we discuss the structural diversity and biogenesis of dipeptides, with respect to (i) proteinogenic dipeptides that are products of protein degradation, (ii) non-proteinogenic amino acid dipeptides, such as those containing a γ-glutamyl group, and (iii) cyclic dipeptides, largely derived from microorganisms. Highlighted are recent examples of dipeptides that were shown to display plant health-promoting activities, including boosting growth and improving stress resilience against pathogens, salinity, chilling, and heat, making the case that these overlooked compounds are more than what meets the eye.