Chinese wild rice (Zizania latifolia; family: Gramineae) is a valuable medicinal homologous grain in East and Southeast Asia. Here, using Nanopore sequencing and Hi-C scaffolding, we generated a 547.38 Mb chromosome-level genome assembly comprising 332 contigs and 164 scaffolds (contig N50 = 4.48 Mb; scaffold N50 = 32.79 Mb). The genome harbors 38,852 genes, with 52.89% of the genome comprising repetitive sequences. Phylogenetic analyses revealed close relation of Z. latifolia to Leersia perrieri and Oryza species, with a divergence time of 19.7–31.0 million years. Collinearity and transcriptome analyses revealed candidate genes related to seed shattering, providing basic information on abscission layer formation and degradation in Z. latifolia. Moreover, two genomic blocks in the Z. latifolia genome showed good synteny with the rice phytocassane biosynthetic gene cluster. The updated genome will support future studies on the genetic improvement of Chinese wild rice and comparative analyses between Z. latifolia and other plants.

The loss of seed shattering is an important event in crop domestication, and elucidating the genetic mechanisms underlying seed shattering can help reduce yield loss during crop production. This study is the first to systematically identify and analyse the BELL family of transcription factor-encoding genes in Chinese wild rice (Zizania latifolia). ZlqSH1a (Zla04G033720) and ZlqSH1b (Zla02G027130) were identified as key candidate genes involved in seed shattering in Z. latifolia. These genes were involved in regulating the development of the abscission layer (AL) and were located in the nucleus of the cell. Over-expression of ZlqSH1a and ZlqSH1b resulted in a complete AL between the grain and pedicel and significantly enhanced seed shattering after grain maturation in rice. Transcriptome sequencing revealed that 172 genes were differentially expressed between the wild type (WT) and the two transgenic (ZlqSH1a and ZlqSH1b over-expressing) plants. Three of the differentially expressed genes related to seed shattering were validated using qRT-PCR analysis. These results indicate that ZlqSH1a and ZlqSH1b are involved in AL development in rice grains, thereby regulating seed shattering. Our results could facilitate the genetic improvement of seed-shattering behaviour in Z. latifolia and other cereal crops.

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