Peptide Hormones and Regulation of Sources–Sink Regulation

The coordination between source and sink organs in plants is governed by a complex network of signaling pathways, ensuring optimal allocation of photoassimilates in response to developmental cues and environmental conditions. Source tissues, primarily mature leaves, fix carbon via photosynthesis and export sugars, while sink organs, such as young leaves, roots, and reproductive structures, import and utilize these resources for growth. This dynamic source–sink relationship is regulated through sugar signaling, hormonal control, and environmental sensing. Sugars like glucose and sucrose serve dual roles as metabolic substrates and signaling molecules, modulating gene expression and physiological processes. Classical hormones, including auxins, cytokinins, and abscisic acid, further coordinate photosynthesis, phloem loading, and sink development. This chapter focuses on peptide hormones, a specialized class of regulatory molecules playing pivotal roles in source–sink modulation. It outlines their classification, biosynthesis, and signaling pathways, emphasizing the importance of posttranslational modifications (PTMs) in their maturation and activation. This chapter highlights the roles of key peptide hormones, such as CEPs, in regulating phloem transport, nutrient allocation, and the strength of sink. Their function in stress-induced reprogramming of source–sink dynamics is also explored, alongside environmental modulation of peptide signaling. Finally, the chapter discusses the potential of harnessing peptide hormones for crop improvement and yield enhancement and provides insights into current challenges and future research directions in the field.