ARGONAUTE2 Enhances Grain Length and Salt Tolerance by Activating to Modulate Cytokinin Distribution in Rice.

Maintaining stable, high yields under fluctuating environmental conditions is a long-standing goal of crop improvement but is challenging due to internal trade-off mechanisms, which are poorly understood. Here, we identify ARGONAUTE2 (AGO2) as a candidate target for achieving this goal in rice (). Overexpressing led to a simultaneous increase in salt tolerance and grain length. These benefits were achieved via the activation of (), encoding a purine permease potentially involved in cytokinin transport. AGO2 can become enriched on the locus and alter its histone methylation level, thus promoting expression. Cytokinin levels decreased in shoots but increased in roots of -overexpressing plants. While knockout mutants were hypersensitive to salt stress, plants overexpressing showed strong salt tolerance and large grains. The knockout of significantly reduced grain length and salt tolerance in -overexpressing plants. Both genes were transcriptionally suppressed by salt treatment. Salt treatment markedly increased cytokinin levels in roots but decreased them in shoots, resulting in a hormone distribution pattern similar to that in -overexpressing plants. These findings highlight the critical roles of the spatial distribution of cytokinins in both stress responses and grain development. Therefore, optimizing cytokinin distribution represents a promising strategy for improving both grain yield and stress tolerance in rice.