Suppressing a phosphohydrolase of cytokinin nucleotide enhances grain yield in rice.

One-step and two-step pathways are proposed to synthesize cytokinin in plants. The one-step pathway is mediated by LONELY GUY (LOG) proteins. However, the enzyme for the two-step pathway remains to be identified. Here, we show that quantitative trait locus GY3 may boost grain yield by more than 20% through manipulating a two-step pathway. Locus GY3 encodes a LOG protein that acts as a 5'-ribonucleotide phosphohydrolase by excessively consuming the cytokinin precursors, which contrasts with the activity of canonical LOG members as phosphoribohydrolases in a one-step pathway. The residue S41 of GY3 is crucial for the dephosphorylation of iPRMP to produce iPR. A solo-LTR insertion within the promoter of GY3 suppressed its expression and resulted in a higher content of active cytokinins in young panicles. Introgression of GY3 increased grain yield per plot by 7.4% to 16.3% in all investigated indica backgrounds, which demonstrates the great value of GY3 in indica rice production.