Regulation of vacuole fusion, a pivotal mechanism mitigating salt-induced inhibition of root cell growth

Vacuoles are essential for plant growth and morphogenesis. Vacuoles fused under normal conditions, promoting cell elongation and organ growth. Changes in vacuole dynamics affect root growth, but how these dynamics are modulated during stress remains unclear. We found that short-term exposure to low-salt concentrations decreases root growth, primarily impairing root cell elongation. In root cells, vacuole fusion consistently decreases despite an increase in the overall vacuole volume. Accordingly, RABG3f, which regulates the formation of tethering complexes necessary for fusion, is retained at enlarged endosomes. Genetic interference of the vacuole fusion machinery results in salt-insensitive root phenotypes that are reversed by the pharmacological induction of vacuole fusion. Importantly, these mutants recover root growth more efficiently after salt stress, indicating that vacuole fusion inhibition serves as a protective mechanism. This fundamental mechanism may serve broader roles in stress tolerance by inhibiting fusion, increasing vacuole convolution, and mitigating stress impact on root growth.