Tubulin Cytoskeleton Reorganization During Development of Arachis hypogaea L. Nodules

The cellular mechanisms underlying nodulation in peanut (Arachis hypogaea L.), which proceeds via an infection-thread-independent intercellular pathway, remain poorly understood relative to those in model legumes. Because microtubules provide the intracellular framework for organelle positioning, nuclear migration, and cell-wall remodeling, they are likely to play a central role in the host-cell reorganization required for rhizobial accommodation. This study examined the spatial and temporal reorganization of microtubules during nodule development in peanut cv. ‘Valencia 433’ inoculated with Bradyrhizobium ottawaense strain RCAM104, following host-cell remodeling from early primordia to mature nodules. Prior to rhizobial entry, cortical microtubules in primordium cells displayed a regular arrangement (transversely oriented microtubules arranged perpendicularly to the longitudinal axis of the cell), which became locally disorganized at bacterial entry sites, accompanied by the presence of the host nucleus near the penetration site. During host cell mitosis, symbiosomes exhibited a coordinated redistribution that aligned with mitotic spindle and phragmoplast dynamics. In young infected cells, cortical microtubules retained a regular pattern, whereas endoplasmic microtubules formed a randomly oriented network. Upon bacteroid differentiation from the U-type to the S-type morphology, cortical microtubules reorganized into an irregular, randomly oriented network. These findings demonstrate that early microtubule responses to intercellular entry share features with conserved symbiotic penetration mechanisms. In contrast, the subsequent shift from a regular to an irregular cortical array—partially resembling that observed in indeterminate nodules—correlates with bacteroid morphological differentiation, highlighting unique cellular dynamics in peanut nodules.