cGMP signalling transduction pathways cross talk with first and second messengers in plants

The 3′,5′-cyclic guanosine monophosphate (cGMP) signalling cascade transmits highly diverse and complex biological signals and serves as a key regulator of cellular homeostasis. cGMP is synthesized by guanylate cyclase (GC) from guanosine triphosphate (GTP) and hydrolysed to 5'-GMP by phosphodiesterase (PDE). In plants, cGMP acts as a second messenger involved in physiological processes, including seed germination, root development, pollen tube growth, photosynthesis and defence responses; it mediates signal transduction from first messengers such as plant hormones, including gibberellin (GA), auxin (IAA), and abscisic acid (ABA), and environmental changes (temperature, light, water and salt stress). cGMP is not only regulated by many hormones but also exerts reverse regulatory effects on phytohormones; in addition, it interacts closely with a variety of second messengers, such as nitric oxide (NO) and calcium ions (Ca 2+ ). The upstream and downstream relationships between cGMP and first and second messengers are complex and diverse. This article comprehensively reviews the biological functions of cGMP in plants and its upstream signalling substances, downstream effectors and target proteins; analyses the complex relationships between cGMP and its first messengers and second messengers; describes the signalling pathways through which cGMP regulates plant growth and development; and discusses existing problems and future prospects, aiming to provide valuable references for advancing the in-depth study of cGMP signalling mechanisms and their utilization in plants.