The stay-green phenotype of TaNAM-RNAi wheat plants is associated with maintenance of chloroplast structure and high enzymatic antioxidant activity

Abstract

SummaryTaNAM transcription factors play an important role in controlling senescence, which in turn, influences the delivery of nitrogen, iron and other elements to the grain of wheat (Triticum aestivum) plants, thus contributing to grain nutritional value. While lack or diminished expression of TaNAMs determines a stay-green phenotype, the precise effect of these factors on chloroplast structure has not been studied. In this work we focused on the events undergone by chloroplasts in two wheat lines having either control or diminished TaNAM expression due to RNA interference (RNAi). It was found that in RNAi plants maintenance of chlorophyll levels and maximal photochemical efficiency of photosystem II were associated with lack of chloroplast dismantling. Flow cytometer studies and electron microscope analysis showed that RNAi plants conserved organelle ultrastructure and complexity. It was also found that senescence in control plants was accompanied by a low leaf enzymatic antioxidant activity. Lack of chloroplast dismantling in RNAi plants was associated with maintenance of protein and iron concentration in the flag leaf, the opposite being observed in control plants. These data provide a structural basis for the observation that down regulation of TaNAMs confers a functional stay-green phenotype and indicate that the low export of iron and nitrogen from the flag leaf of these plants is concomitant, within the developmental window studied, with lack of chloroplast degradation and high enzymatic antioxidant activity. 3 Highlights•TaNAM-RNAi stay-green phenotype is coupled with maintenance of chloroplast structure.•That stay-green phenotype is associated with a high enzymatic antioxidant activity.•Chloroplast dismantling correlates with decay of iron and protein content in leaves.

Efficient Physiological and Nutrient Use Efficiency Responses of Maize Leaves to Drought Stress under Different Field Nitrogen Conditions

“…Currently, a broadly accepted perspective is that higher N levels of leaves are associated with delayed leaf senescence, which confers improved drought tolerance [11,36,37]. The decrease of yield between drought and nondrought stress increased with increasing N treatment rates.…”

“…Episodes of intense and prolonged drought are projected to surge worldwide due to future global warming/climate change [9]. Under drought stress, the inhibition of carbohydrate assimilation 2 of 14 or its export from sources organs may result in superfluous photosynthetic light energy, which may consequently induce the intense generation of reactive oxygen species (ROS) in leaves [10,11]. Subsequently, drought stress induces alterations in physiological status and disturbances in metabolism homeostasis, which deleteriously influence plant growth and development, including a marked suppression in the photosynthetic efficiencies of plants [12] and the depolarization of plasma membranes [13].…”

Transcriptome Analysis of a Premature Leaf Senescence Mutant of Common Wheat (Triticum aestivum L.)

“…GPC-B1 is an NAC family transcription factor that accelerates leaf senescence and affects the protein, zinc, and iron contents of wild wheat grains [ 27 ]. TaNAMs were down-regulated by RNAi technology, which led to the stay-green phenotype and the reduction in nutritive material transport from flag leaves to seeds [ 38 ]. The difficulty that is associated with wheat gene studies is caused by the complexity of the huge wheat genome, with a high ratio of repeat sequences [ 39 ].…”

Ferric-chelate reductase OsFRO1 involved in Fe reduction and long distance Fe transport channelized by OsYSL2 and OsYSL15 in rice

“…It was found that TaNAM-RNAi plants maintained maximal photochemical e ciency modulated enzymatic network accompanied by low nitrogen and iron (Fe) concentration in ag leaf, suggesting that RNAi plants have more tolerance against Fe stress at certain level (Checovich et al, 2016). A quite similar pattern was also noted in the OsFRO1-RNAi plants.…”