Altered Fruit and Seed Development of Transgenic Rapeseed (Brassica napus) Over-Expressing MicroRNA394.

Fruit and seed development in plants is a complex biological process mainly involved in input and biosynthesis of many storage compounds such as proteins and oils. Although the basic biochemical pathways for production of the storage metabolites in plants are well characterized, their regulatory mechanisms are not fully understood. In this study, we functionally identified rapeseed (Brassica napus) miR394 with its target gene Brassica napus leaf curling responsiveness (BnLCR) to dissect a role of miR394 during the fruit and seed development. Transgenic rapeseed plants over-expressing miR394 under the control of the cauliflower mosaic virus 35S promoter were generated. miR394 over-expression plants exhibited a delayed flowering time and enlarged size of plants, leaf blade, pods and seed body, but developed seeds with higher contents of protein and glucosinolates (GLS) and lower levels of oil accumulation as compared to wild-type. Over-expression of miR394 altered the fatty acid (FA) composition by increasing several FA species such as C16:0 and C18:0 and unsaturated species of C20:1 and C22:1 but lowering C18:3. This change was accompanied by induction of genes coding for transcription factors of FA synthesis including leafy cotyledon1 (BnLEC1), BnLEC2, and FUSCA3 (FUS3). Because the phytohormone auxin plays a crucial role in fruit development and seed patterning, the DR5-GUS reporter was used for monitoring the auxin response in Arabidopsis siliques and demonstrated that the DR5 gene was strongly expressed. These results suggest that BnmiR394 is involved in rapeseed fruit and seed development.