Polyamines, are small, positively charged molecules that play vital roles in cell growth, development, and various fundamental cellular processes in all living cells. Besides the most abundant and well-studied polyamines, some less plenteous polyamines also exist with specific roles. These include for example agmatine, cadaverine, and thermospermine. Additionally, some organisms, particularly thermophilic bacteria and archaea, contain a wider variety of polyamines with longer chains and branched structures. Over the past two decades, polyamines have been increasingly studied and gained significant attention due to their pivotal role in stress responses. Despite advancements, the understanding of the complex interactions and specific genetic pathways influenced by polyamines remains incomplete, necessitating further exploration into their multifaceted roles.

This Research Topic aims to delve into the intricacies of polyamine functions in promoting resilience in plants subjected to abiotic stress, such as drought, salinity, and extreme temperatures or in plant and fungi or bacteria interactions (exhibiting both positive and negative effects). Most of the signalling pathways involved in responses to abiotic and biotic stresses share common elements that are potential nodes of crosstalk. Such common elements may serve as major switching points and play a role in stress tolerance. It is increasingly clear that polyamines are also such switching points, and that polyamine-induced responses are interconnected at many levels.

However, it should be also taken into consideration, that the polyamine metabolism is dynamic, putrescine, spermidine and spermine can be rapidly converted into each other in the polyamine cycle. Furthermore, polyamine metabolism is also linked to the synthesis of plant hormones and other signaling molecules, such as NO, H2O2, or GABA; furthermore, their catabolism is also linked to the C and N metabolism.

By examining polyamine metabolism and signaling at the crossroads of growth, development and stress, the research featured in this research topic seeks to identify and illuminate the genetic and molecular mechanisms that facilitate plant viability and stress tolerance. Additionally, the topic will explore how manipulating polyamine levels could enhance stress tolerance and improve agricultural productivity, addressing pivotal questions on the modulation of these pathways and their practical applications.

To gather further insights in the dynamic role of polyamines, we welcome articles addressing, but not limited to, the following themes:

• Polyamine metabolism and functions in different plant species influenced by various circumstances
• Role of polyamines in plant-pathogen interactions or symbiotic associations
• The interactions between polyamine metabolism and hormonal signaling
• Genetic pathways or metabolic shifts activated by polyamines during stress
• Innovative biotechnological approaches to modulate polyamine pathways for improved stress resilience

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The Polyamine Nexus: The Crossroads of Growth, Development, and Stress in Plants and Fungi