Spatiotemporal orchestration of phytohormones determines the organization pattern of aerenchyma in S. polyrhiza
Aerenchyma is crucial for plant adaptation to stresses like hypoxia, drought, and nutritional deficiency. Although ethylene-mediated signaling cascades are known to regulate aerenchyma formation under hypoxic conditions, the precise mechanisms are still unclear. Moreover, cellular dynamics underlying the process of aerenchyma formation are still not well understood. We investigated the stage-dependent structural dynamics of aerenchyma in Spirodela polyrhiza (S. polyrhiza), a fast-growing aquatic herb with well-developed aerenchyma in its floating fronds. Using X-ray micro-computed tomography and histological analysis, we found that the spatial framework of aerenchyma was established before frond volume increased, driven by cell division and expansion. Additionally, the substomatal cavity connecting aerenchyma to stomata is formed via programmed cell death (PCD) closely associated with guard cell development. Transcriptome analysis and pharmacological studies further revealed that the organization of aerenchyma in S. polyrhiza is determined by the interplay between PCD and proliferation. This balance was governed by the spatiotemporal regulation of phytohormone signaling, including ethylene, abscisic acid, and salicylic acid. Our study sheds light on the structural dynamics and hormonal regulation of aerenchyma development in duckweeds, improving understanding of plant responses to environmental stresses and providing potential avenues for enhancing crop resilience under climate change. Overall design: RNA sequencing of frond tissues of Spirodela polyrhiza plants at development stages 2-6 (n=3 for stages 2-4 and n=2 for stages 5-6)