The basic helix‐loop‐helix transcription factor, OsPIL15, regulates grain size via directly targeting a purine permease gene OsPUP7 in rice

Summary As members of the basic helix‐loop‐helix transcription factor families, phytochrome‐interacting factors regulate an array of developmental responses ranging from seed germination to plant growth. However, little is known about their roles in modulating grain development. Here, we firstly analyzed the expression pattern of rice Os PIL genes in grains and found that Os PIL 15 may play an important role in grain development. We then generated knockout ( KO ) Os PIL 15 lines in rice using CRISPR /Cas9 technology, the silencing expression of Os PIL 15 led to increased numbers of cells, which thus enhanced grain size and weight. Moreover, overexpression and suppression of Os PIL 15 in the rice endosperm resulted in brown rice showing grain sizes and weights that were decreased and increased respectively. Further studies indicated that Os PIL 15 binds to N1‐box ( CACGCG ) motifs of the purine permease gene Os PUP 7 promoter. Measurement of isopentenyl adenosine, a bioactive form of cytokinin ( CTK ), revealed increased contents in the Os PIL 15 ‐ KO spikelets compared with the wild‐type. Overall, our results demonstrate a possible pathway whereby Os PIL 15 directly targets Os PUP 7 , affecting CTK transport and thereby influencing cell division and subsequent grain size. These findings provide a valuable insight into the molecular functions of Os PIL 15 in rice grains, highlighting a useful genetic improvement leading to increased rice yield.