Bulliform cells: anatomical, physiological, genetic, and computational perspectives on plants' drought adaptation

This work highlights pollen thermotolerance as vital for reproductive success under heat stress, integrating molecular regulation, gene mapping, and breeding strategies to accelerate development of resilient, high-yielding crop varieties. Bulliform cells are specialized epidermal motor cells predominantly found on the adaxial surface of grass leaves and play a crucial role in mediating adaptive leaf rolling under water deficit conditions. This dynamic morphophysiological response reduces the exposed surface area, minimizes transpirational water loss, and creates favorable microclimatic conditions for photosynthetic tissues, thereby enhancing drought tolerance. This review highlights molecular regulation as a central component of bulliform cell function and integrates it with morphological, anatomical, physiological, and hormonal responses. Recent studies have identified genetic and hormonal regulators of bulliform cell development, including key transcription factors such as SRL1, ROC1, ACL1/2, as well as phytohormones including abscisic acid (ABA), cytokinins (CKs), and brassinosteroids (BRs), revealing a complex integration of developmental and stress-responsive pathways. Advances in high-resolution imaging, single-cell transcriptomics, and machine learning provide mechanistic insights into bulliform cell-specific gene expression, turgor dynamics, and structural contributions to leaf rolling. Quantitative analyses, including genome-wide association studies (GWAS) and quantitative trait locus (QTL) mapping, have associated BC traits with leaf rolling indices, water-use efficiency, and drought tolerance in cereals. Despite these advances, significant knowledge gaps remain, particularly regarding how bulliform cells respond to combined abiotic stresses and the physiological trade-offs between water conservation and leaf thermoregulation. This review presents a novel, integrative framework of multi-omics, systems biology, and AI-driven modeling to develop predictive insights into bulliform cell behavior to optimize their anatomical and physiological traits for enhanced crop resilience. In addition, this review integrates current anatomical, physiological, genetic, and computational insights into bulliform cells, revealing their pivotal role in plant adaptation and their emerging potential as targets for developing stress-resilient crops.