The amazing QQS!
On the final morning of the recent ICAR2016 meeting attendance was rather low, seemingly after a heavy karaoke-filled night! However those that got out of bed had to pleasure of attending the excellent ‘Plant Biotechnology’ session, which provided great insights into the process of developing and bringing plant products to the market.
However for me it was a more ‘conventional’ presentation that was a real eye-opener. Li Ling from Iowa State University introduced the QQS gene that is an orphan gene only present in Arabidopsis. This small loci has no previously characterised domains and was identified during expression analysis of genes that are upregulated in a strach synthase mutant. Although it is small and mysterious, the QQS gene appears to play a remarkably role in the control of plant carbon-nitrogen balance. Arabidopsis plants that overexpress QQS show a significant decrease in leaf starch content and an associated increase in overall leaf protein content. This occurs without any phenotypic change or yield penalty.
Li Ling subsequently overexpressed QQS in soybean and also showed, even though plants were again morphologically identical to wildtype, an increase in seed protein and only a slight decline in seed oil content. Remarkably this is occuring in plants that have been previously ‘seen’ the QQS gene and this effect occurs independent of growth location (greenhouse, field) or soil nitrogen content. Similar results have been also found when QQS is overexpressed in maize and rice.
In more recent experiments Ling and co-workers discovered that QQS acts upstream of the AtNF-YC4 gene in Arabidopsis and that overexpression of AtNF-YC4 also causes an increase in protein content and a decrease in starch. Soybean, maize and rice each contain orthologs of AtNF-YC4, demonstrating that the signalling module is preserved in these distantly related crops. Li mentioned that attempts to modify the expression NF-YC4 in crop plants using gene-editing techniques are at an advanced stage, which will hopefully lead to the generation of transgene-free plants that have increased protein content. Furthermore Li reported that the QQS:NF-Y4 module influences multiple aspects of the response to pathogens, work which will be published soon and further demonstrates the pleiotropic nature of QQS function.
Overall the QQS gene has remarkably potential for use in experiments that aim to generate plants with altered C/N balance. It seems that even though Arabidopsis, soybean, maize and rice are evolutionarily divergent, they each retain the ability to respond to the QQS protein via the NF-YC4 signaling module.
As the authors state, the yield-altering effects of this response pathway have broad societal importance and hopefully can be used in the generation of crops with different nutritional attributes.
On a smaller scale, this work with an orphan gene should also offer encouragement to researchers who have identified a gene with ‘no known function’ from their particular mutant screen! If you persevere, you never know where it might lead!
Leave a Reply