Altered flower architecture for better photosynthesis in canola

Analysis of the pDAP3-AP1::hpBPI in B. napus flowers (a) C24 Arabidopsis wild-type mature flower (b) Mature transgenic flower. Second-whorl organs are sepals (arrow) that are slightly smaller than the true sepals. Morphological features of Brassica napus flowers: mature wild-type flower (left), mature flower of a transgenic plant (right).  The second-whorl organs of a transgenic flower are yellowish-green sepaloid petals (arrow). The size of these organs is similar to sepals developed in the first whorl, but the lamina-base structure can still be distinguished (for comparison see the detached organs in the bottom right corner: the second-whorl organ (left), the first-whorl organ (right) of a transgenic flower).

Canola (Brassica napus L.) genotypes with no or small petals are thought to have advantages in photosynthetic activity. The flowers of field-grown canola form a bright-yellow canopy that reflects and absorbs nearly 60 per cent of the photosynthetically active radiation (PAR), causing a severe yield penalty. Reducing the size of the petals and/or removing the reflecting colour will improve the transmission of PAR to the leaves and is expected to increase the crop productivity.

HairpinRNAi silencing of BPI gene family (MADS-box floral organ identity genes) was achieved by expressing a hairpinRNAi construct under the control of a chimeric promoter consisting of a modified petal-specific Arabidopsis AP3 promoter fragment fused to the AP1 promoter.

In this way, transgenic plants were generated producing male fertile flowers in which the petals were converted into sepaloid petals. These novel flower phenotypes were stable and heritable in both species.

(Byzova et al., 2004, Planta 218, 379-387)