Overexpression of a NAC transcription factor delays leaf senescence and increases grain nitrogen concentration in wheat

Abstract

Increasing the duration of leaf photosynthesis during grain filling using slow‐senescing functional stay‐green phenotypes is a possible route for increasing grain yields in wheat (Triticum aestivum L.). However, delayed senescence may negatively affect nutrient remobilisation and hence reduce grain protein concentrations and grain quality. A novel NAC1‐type transcription factor (hereafter TaNAC‐S) was identified in wheat, with gene expression located primarily in leaf/sheath tissues, which decreased during post‐anthesis leaf senescence. Expression of TaNAC‐S in the second leaf correlated with delayed senescence in two doubled‐haploid lines of an Avalon × Cadenza population (lines 112 and 181), which were distinct for leaf senescence. Transgenic wheat plants overexpressing TaNAC‐S resulted in delayed leaf senescence (stay‐green phenotype). Grain yield, aboveground biomass, harvest index and total grain N content were unaffected, but NAC over‐expressing lines had higher grain N concentrations at similar grain yields compared to non‐transgenic controls. These results indicate that TaNAC‐S is a negative regulator of leaf senescence, and that delayed leaf senescence may lead not only to increased grain yields but also to increased grain protein concentrations.

Mapping QTL associated with remobilization of zinc from vegetative tissues into grains of barley (Hordeum vulgare)

“…Gpc-B1 ortholog genes are identified in barley, and leaf senescence in both barley and wheat is considered to regulate grain protein content, nutrient remobilization and grain yield (Distelfeld et al 2014). Phylogenetic NAC transcriptional factor TaNAC-S, identified by Zhao et al (2015) in wheat, delayed leaf senescence and increased grain yield, N remobilization into grains and grain protein concentration. Expression of other transcript factors of NAC gene in wheat, such as NAM genes, also regulated remobilization of Fe, Zn and N from the vegetative tissues to grains (Waters et al 2009).…”

Living to Die and Dying to Live: The Survival Strategy behind Leaf Senescence

“…In rice, loss of OsNAP results in the delayed onset of senescence and a concomitant 6% to 10% increase in grain yield in the field . However, in Triticum aestivum, overexpression of TaNAC-S delays leaf senescence, resulting in an increased N content in the grain, but it has no effect on total yields (Zhao et al, 2015), indicating that delayed senescence does not always improve productivity. In a field experiment using four different maize lines displaying altered onset of leaf senescence, grain yields were similar, but N contents were lower, under nonstress conditions (Acciaresi et al, 2014).…”

Early anthesis and delayed but fast leaf senescence contribute to individual grain dry matter and water accumulation in wheat

“…In addition, it could also be possible to increase grain protein concentration for improved grain quality through stay-green phenotype (Bogard et al, 2011). An example is overexpressing some particular NAC transcription factors (Zhao et al, 2015).…”