The OsbZIP35-COR1-OsTCP19 module modulates cell proliferation to regulate grain length and weight in rice.

Abstract

Grain size substantially influences rice quality and yield. In this study, we identified <i>CONTROL OF SLENDER RICE 1</i> (<i>COR1</i>), a quantitative trait locus encoding an F-box protein that enhances grain length by promoting cell proliferation. The transcription factor OsbZIP35 represses <i>COR1</i> expression, while COR1 interacts with OsTCP19, leading to its degradation. Knockout of either <i>OsbZIP35</i> or <i>OsTCP19</i> results in increased grain length, confirming their regulatory roles in grain development. The OsbZIP35-COR1-OsTCP19 module controls the expression of the cell cycle gene <i>OsCycB1;4</i>, thereby modulating cell proliferation and ultimately determining grain size. Five haplotypes of <i>COR1</i> were identified, with <i>COR1</i>-Hap1 and <i>COR1</i>-Hap3 being elite alleles associated with longer grains. Field plot trials demonstrated that the near-isogenic line NIL-<i>COR1</i>^SLG increased yield by ~6.6% compared to NIL-<i>COR1</i>^Nip. These findings elucidate the genetic mechanisms underlying grain size regulation and offer promising strategies for improving rice yield.