Dear Editor,
Grain length (size) and weight are essential components of crop yield. To date, many QTLs/genes for these traits have been identified. GS3 encodes a putative transmembrane protein and functions as a negative regulator, and its larger-grain allele contains a nonsense mutation causing a 178-aa truncation (Fan et al., 2006). GL3.1/qGL3 encodes a putative protein phosphatase and also acts as a negative regulator of grain size (Qi et al., 2012, Zhang et al., 2012). Another negative regulator of grain size and weight is TGW6, which hydrolyzes indole-3-acetic acid (IAA)-glucose into IAA and glucose (Ishimaru et al., 2013). In contrast, GW6a is a positive regulator of grain weight, which encodes a novel histone H4 acetyltransferase (Song et al., 2015). Copy number variation at the GL7/GW7 locus causes elevated expression of GL7 and thus an increase in grain length (Wang et al., 2015a, Wang et al., 2015b). GL2/GS2 encodes the plant-specific transcription factor OsGRF4, and its larger-grain allele harbors a mutation preventing cleavage by miR396c, resulting in elevated GL2/GS2 expression (Hu et al., 2015, Che et al., 2016). GLW7 encodes the plant-specific transcription factor OsSPL13, and high OsSPL13 expression is associated with larger grains (Si et al., 2016). These findings have greatly enhanced our understanding of grain length and weight regulation; however, there are still gaps in integrating these factors into genetic network(s). Here, we report a thorough dissection of the QTL composition of grain size and the characterization of a novel QTL, qTGW3, that regulates grain length and weight in rice.