SHORT HYPOCOTYL UNDER BLUE 1 or HAIKU 2 mixepression alters canola and Arabidopsis seed development

Summary Canola ( Brassica napus ) is a widely cultivated species and provides important resources of edible vegetable oil, biodiesel production and animal feed. Seed development in Arabidopsis and canola shares a similar path: an early proliferation of endosperm to form a large seed cavity, followed by a second phase in which the embryo grows to replace the endosperm. In Arabidopsis, the seed reaches almost its final volume before the enlargement of the embryo. SHORT HYPOCOTYL UNDER BLUE 1 ( SHB 1 ) is a key regulatory gene of seed development with a broad expression beyond endosperm development. By contrast, its two target genes, MINISEED 3 ( MINI 3 ) and HAIKU 2 ( IKU 2 ), are narrowly expressed in early developing endosperm and early embryo. We overexpressed SHB 1 in canola to explore the possibility of altering seed development. As an alternative strategy, we expressed the canola IKU 2 ortholog in Arabidopsis endosperm under the control of a stronger MINI 3 promoter. SHB 1 targeted canola orthologs of Arabidopsis MINI 3 and IKU 2 and caused a significantly increased seed mass. Overaccumulation of IKU 2 in the early stage of Arabidopsis seed development also significantly increased the final seed mass. Our studies provide a strong case for increasing the final seed mass by manipulating endosperm proliferation at a rather early developmental stage in crops.