Enhanced expression of OsNAC5 leads to up-regulation of OsNAC6 and changes rice (Oryza sativa L.) ionome

NAC transcription factors are plant-specific proteins involved in many processes during the plant life cycle and responses to biotic and abiotic stresses. Previous studies have shown that stress-induced OsNAC5 from rice (Oryza sativa L.) is up-regulated by senescence and might be involved in control of iron (Fe) and zinc (Zn) concentrations in rice seeds. Aiming a better understanding of the role of OsNAC5 in rice plants, we investigated a mutant line carrying a T-DNA insertion in the promoter of OsNAC5 , which resulted in enhanced expression of the transcription factor. Plants with OsNAC5 enhanced expression were shorter at the seedling stage and had reduced yield at maturity. In addition, we evaluated the expression level of OsNAC6 , which is co-expressed with OsNAC5 , and found that enhanced expression of OsNAC5 leads to increased expression of OsNAC6 , suggesting that OsNAC5 might regulate OsNAC6 expression. Ionomic analysis of leaves and seeds from the OsNAC5 enhanced expression line revealed lower Fe and Zn concentrations in leaves and higher Fe concentrations in seeds than in WT plants, further suggesting that OsNAC5 may be involved in regulating the ionome in rice plants. Our work shows that fine-tuning of transcription factors is key when aiming at crop improvement.

Automated summary

This study found that stress-induced OsNAC5 in rice is up-regulated by senescence and might be involved in regulating iron and zinc concentrations in rice seeds. Overexpression of OsNAC5 resulted in shorter seedlings, reduced yield, and increased expression of OsNAC6. Analysis showed that overexpression of OsNAC5 led to lower iron and zinc concentrations in leaves and higher iron concentrations in seeds. Fine-tuning of transcription factors is therefore crucial for crop improvement.