Construction of transgenic lines

The amiR‐MGD1 construct was described previously (Fujii et al., 2014). Wild‐type and dgd1‐1 plants were transformed with the amiR‐MGD1 construct by Agrobacterium tumefaciens‐mediated transformation. Five and 13 T1 transgenic lines were obtained in the Col and dgd1‐1 backgrounds, respectively. T2 seeds were harvested individually from these T1 lines. Lines showing c. 75% Basta (selection marker for the amiR‐MGD1 construct) resistance were considered as having a single‐copy transgene insertion. We then harvested seeds of the T3 generation from individual plants. Lines showing 100% Basta resistance were considered homozygous for the transgene.