Sporophytic control of male fertility, the role of the SWEET4 gene in barley

A vital process for plant growth and differentiation is represented sugar distribution. The long-distance movement of sugar occurs form source to sink tissues; afterwards, sugar is further distributed following extra- cellular and intra-cellular pathways. Sugars are translocated thr symplastic and apoplastic routes, the latter needs the activity of specific transport proteins. The SWEET (Sugar Will Eventually Exported Protein) gene family is the most recent identified group of sugar transporters in 201 (Chen at al.). The presence of this gene family was confirmed in all th eukaryotic kingdoms, and in prokaryotes. Eukaryotic SWEET proteins characterized by seven predicted transmembrane (TM) domains forming a pore where sugars are predicted to move following their concentration gradient. Focusing the attention on the barley genome, we have identified 23 SWEE sequences which contained the expected TM domainsH;vSWEET genes can be further grouped into four clades, as already observed for this gene family in different Angiosperm genomes. It was proposed that belonging t specific clade correlates with the selectivity toward monosacchar versus disaccharides (Eom et al., 2015). Our group is interested in identifying genes that can be manipulated increase specific yield components. For this reason, we focused attention on theHvSWEET4 (HvSW4) gene whose maize and rice orthologous play an important role during the seed filling process; both these gene appeared to be recruited during domestication to enhance the hexose import into the developing endosperm (Sosso et al., 2015). To highlight functional role of the HvSW4 gene, we created the sw4 mutant through genome editing in the golden promise genetic background. Interestingly, our data indicate that, in barley, the HvSW4 gene acquired a novel function related to the sporophytic control of male fertility. Morphological analysis mutant flowers shows that early stages of pollen maturation are affecte due to lack of activity of the HvSW4 protein, while kernel development is not altered likely due to functional redundancy with other SWEET proteins and/or other sugar transporters. Further analyses are currently ongoing to better dissect the molecular pathways influenced by the HvSW4 activity and to identify the transcriptional regulators.