Synthesis and accumulation of plant oils in the entire vegetative biomass offers the potential to deliver yields surpassing those of oilseed crops. However, current levels still fall well short of those typically found in oilseeds. Here we show how transcriptome and biochemical analyses pointed to a futile cycle in a previously established Nicotiana tabacum line, accumulating up to 15% (dry weight) of the storage lipid triacylglycerol in leaf tissue. To overcome this metabolic bottleneck, we either silenced the SDP1 lipase or overexpressed the Arabidopsis thaliana LEC2 transcription factor in this transgenic background. Both strategies independently resulted in the accumulation of 30-33% triacylglycerol in leaf tissues. Our results demonstrate that the combined optimization of de novo fatty acid biosynthesis, storage lipid assembly and lipid turnover in leaf tissue results in a major overhaul of the plant central carbon allocation and lipid metabolism. The resulting further step changes in oil accumulation in the entire plant biomass offers the possibility of delivering yields that outperform current oilseed crops.

Flowering (inflorescence formation) of the grass Lolium temulentum is strictly regulated, occurring rapidly on exposure to a single long day (LD). During floral induction, L. temulentum differs significantly from dicot species such as Arabidopsis in the expression, at the shoot apex, of two APETALA1 (AP1)-like genes, LtMADS1 and LtMADS2, and of L. temulentum LEAFY (LtLFY). As shown by in situ hybridization, LtMADS1 and LtMADS2 are expressed in the vegetative shoot apical meristem, but expression increases strongly within 30 h of LD floral induction. Later in floral development, LtMADS1 and LtMADS2 are expressed within spikelet and floret meristems and in the glume and lemma primordia. It is interesting that LtLFY is detected quite late (about 12 d after LD induction) within the spikelet meristems, glumes, and lemma primordia. These patterns contrast with Arabidopsis, where LFY and AP1 are consecutively activated early during flower formation. LtMADS2, when expressed in transgenic Arabidopsis plants under the control of the AP1 promoter, could partially complement the organ number defect of the severe ap1-15 mutant allele, confirming a close relationship between LtMADS2 and AP1.

Arabidopsis flowers in long day (LD) in response to signals transported from the photoinduced leaf to the shoot apex. These LD signals may include protein of the gene FLOWERING LOCUS T (FT) while in short day (SD) with its slower flowering, signalling may involve sucrose and gibberellin. Here, it is shown that after 5 weeks growth in SD, a single LD up-regulated leaf blade expression of FT and CONSTANS (CO) within 4–8 h, and flowers were visible within 2–3 weeks. Plants kept in SDs were still vegetative 7 weeks later. This LD response was blocked in ft-1 and a co mutant. Exposure to different LD light intensities and spectral qualities showed that two LD photoresponses are important for up-regulation of FT and for flowering. Phytochrome is effective at a low intensity from far-red (FR)-rich incandescent lamps. Independently, photosynthesis is active in an LD at a high intensity from red (R)-rich fluorescent lamps. The photosynthetic role of a single high light LD is demonstrated here by the blocking of the flowering and FT increase on removal of atmospheric CO2 or by decreasing the LD light intensity by 10-fold. These conditions also reduced leaf blade sucrose content and photosynthetic gene expression. An SD light integral matching that in a single LD was not effective for flowering, although there was reasonable FT-independent flowering after 12 SD at high light. While a single photosynthetic LD strongly amplified FT expression, the ability to respond to the LD required an additional but unidentified photoresponse. The implications of these findings for studies with mutants and for flowering in natural conditions are discussed.