It has been reported that Gn1a (OsCKX2), one of the genes involved in cytokinin degradation, is crucial for plant growth, determining the number of grains [1]. In this study, we used the indica variety ''IR 64'', a high-yielding mega variety, to create a modified line with enhanced sink capacity, a factor that determines yield. We report the effects of these Gn1a-knockout (KO) lines on sink capacity and yield components in field-grown plants.
The Gn1a-KO line was created by introducing mutations into Gn1a using the CRISPR/Cas9 system. They were filed-tested for cultivation at an isolated field in NARO (Tsukuba City, Japan). As cultivated lines, some progeny lines in which the mutation was genetically fixed and the expression cassette including Cas9 was removed, were used.
Panicle length tended to increase, with more spikelet per panicle due to increased panicle branch numbers showing a well-characterized phenotypic feature of the Gn1a-KO line. Although the number of panicles showed a decreasing trend compared to the original variety, the total number of spikelets per plant maintained an increasing trend. The Gn1a-KO lines were similar to the original variety in 1000-grain weight, but overall, sink capacity showed an increasing trend. Brown rice yield increased with the sink capacity. The rate of filled spikelet showed a decreasing trend, suggesting that maintaining the rate of filled spikelet and panicle number is effective for further stable yield improvement in Gn1a-KO lines.
This work was partially supported by the Cabinet Office's SIP and commissioned work (JPNP18016) by NEDO.