Mobilisation of nutrients from photosynthesizing tissue to the developing grain in wheat is highly influenced by the timing of senescence onset. As a result, understanding how senescence onset is regulated will be critical in efforts to increase grain nutrient content. NAC transcription factors (e.g. NAM-1, NAC-S1,2) have been shown to regulate monocarpic senescence in wheat and provide a useful entry point for understanding these processes.

We have identified a NAC transcription factor, NAC-3, which is upregulated in senescing flag leaves1. Heterologous expression of NAC-3 in N. benthamiana induces cell-death in the infiltrated tissue and at a significantly higher level that that caused by NAM-1. NAC-3 double mutants in tetraploid wheat, derived from the cv ‘Kronos’ TILLING population, exhibit delayed leaf and peduncle senescence with respect to wild-type plants. We are currently investigating whether this NAC-3 mediated delay in senescence corresponds to variation in grain nutrient content. Intriguingly, we have shown that NAM-1 and NAC-3 interact through Yeast-Two-Hybrid and Co-Immunoprecipitation assays, suggesting they may work together to regulate senescence.

To investigate the possible regulatory overlap between NAC-3 and NAM-1, we used “Genie3” transcriptional networks to identify putative downstream targets shared between the two1. The utility of the Genie3 network predictions was first validated using publicly-available, independent RNA-Seq data from TILLING knock-out lines of the NAM genes2. We found that the Genie3-predicted downstream targets of the NAM genes overlapped with differentially expressed genes significantly more than expected by chance. This suggests that the Genie3 network does provide informative predictions for downstream regulatory targets of transcription factors in polyploid wheat.

Applying the Genie3 network to our genes of interest, we found that NAC-3 and NAM-A1 shared significantly more predicted targets than would be expected by chance, suggesting that they may act on similar biological pathways. We also found that downstream targets of NAC-3 are enriched in senescence-related gene ontology terms, further supporting its role in regulation of monocarpic senescence. These results suggest that the NAC transcription factor NAC-3 plays a role in regulating monocarpic senescence in wheat and may act in tandem with NAM-1.