<i>TavWA1</i> is critical for wheat growth by modulating cell morphology and arrangement

Plant growth is determined by the production of cells and initiation of new organs. Exploring genes that control cell number and cell size is of great significance for understanding plant growth regulation. In this study, we characterized two wheat mutants, ah and dl, with abnormal growth. The ah mutant is a naturally occurring variant characterized by severe dwarfism, increased tiller number, and reduced grain length, while the dl mutant is derived from an ethyl methane sulfonate (EMS)-mutagenized population and exhibits smaller grain size and slightly reduced plant height. Cytological analyses revealed abnormal cell number, cell morphology and arrangement in the stems and leaves of the ah mutant, along with reduced cell length in the grains of the dl mutant. Map-based cloning identified that both mutants carry mutations in the same gene TavWA1-7D, which encodes a protein with a von Willebrand factor A (vWA) domain. The ah mutant harbors a 174-bp insertion in the 1,402-bp coding sequence (CDS) of TavWA1-7D, causing premature termination of protein translation, while the dl mutant contains a Glu420Lys substitution. Mimicking the TavWA1-7D^ah through clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated nuclease 9-mediated genome editing leads to a severe dwarfism phenotype. The C-terminus of the protein is crucial for its correct subcellular localization and interaction, supporting its critical role for TavWA1-7D function. Proteomic analysis showed that the dwarf phenotype of the ah mutant is associated with impaired photosynthesis, ribosome function, and nucleosome formation. Additionally, TavWA1-7D interacts with an E3 ligase, TaVIP1-3B, the expression levels of which are elevated in both mutants. Overexpression and knockout studies of TaVIP1-3B demonstrated its negative regulatory role in cell length and grain size. Together, our findings suggest that TavWA1-7D plays a vital role in regulating wheat growth and yield-related traits, with the dl mutant's short grain phenotype being associated with TaVIP1-3B expression levels.