KAMALA: improved yield by finetuning cytokinin oxidase activity in rice

Abstract

Increasing crop yield is of major importance for food security worldwide. Knock out mutants in the rice cytokinin oxidase gene CKX2 had shown potential for yield improvement. Here we explored whether the Indian mega variety Samba Mahsuri could be improved by introducing mutations into CKX2 by simultaneous editing of two internal sites predicted to subtly impact enzyme activity. Knock out and single in frame mutants generated by CRISPR/Cas12a caused substantial yield increases. Notably, among the 80 CKX2 alleles evaluated, seven lines with different in-frame mutations in both sites produced yield increased up to 98.6% and early flowering. One line, KAMALA, showed superior agronomic performance in 16 of 18 diverse field locations (irrigated and rainfed ecologies) over three seasons in AICRPR trials (All India Coordinated Research Project on Rice), with an average 19% grain yield increase, early maturity, complete panicle emergence, and unaltered grain quality. Notably, in comparison to previously described ckx2 mutants, the KAMALA allele is dominant, indicating unique properties of the variant. KAMALA was registered as the first genome-edited variety ready for cultivation by Indian farmers. 80 tons of KAMALA seeds are available for distribution. A Cas12a license for humanitarian distribution to small and marginal farmers is underway.