Iron (Fe) is an essential micronutrient that is frequently inaccessible to plants. Rice (Oryza sativa L.) plants employ the Combined Strategy for Fe uptake, which is composed by all features of Strategy II, common to all Poaceae species, and some features of Strategy I, common to non-Poaceae species. To understand the evolution of Fe uptake mechanisms, we analyzed the root transcriptomic response to Fe deficiency in O. sativa and its wild progenitor O. rufipogon. We identified 622 and 2,017 differentially expressed genes in O. sativa and O. rufipogon, respectively. Among the genes up-regulated in both species, we found Fe transporters associated with Strategy I, such as IRT1, IRT2 and NRAMP1; and genes associated with Strategy II, such as YSL15 and IRO2. In order to evaluate the conservation of these Strategies among other Poaceae, we identified the orthologs of these genes in nine species from the Oryza genus, maize and sorghum, and evaluated their expression profile in response to low Fe condition. Our results indicate that the Combined Strategy is not specific to O. sativa as previously proposed, but also present in species of the Oryza genus closely related to domesticated rice, and originated around the same time the AA genome lineage within Oryza diversified. Therefore, adaptation to Fe2+ acquisition via IRT1 in flooded soils precedes O. sativa domestication.

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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.

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It is largely known that low temperature stress can affect rice (Oryza sativa L.) development and yield. However, most studies have focussed on unique and uninterrupted cold treatment, which is not representative of cold conditions for early sowing in temperate and subtropical areas where cold nights are followed by warm days during early vegetative stages. In order to elucidate whether rice plants could recover from the damages caused by repetitive cold nights, we submitted a cold-tolerant (CT) and a cold-sensitive (CS) indica genotype to 28 cold nights (10°C) followed by warm days (26°C) and analysed the developmental and productivity traits of plants cultivated in greenhouse and field conditions. While CT plants were able to recover from cold damage without significant development and seed production penalties, CS plants were affected, presenting lower results in plant height, tiller number, number of seeds per plant, % of full seeds per plant, grain length and area, weight of 1000 full grains, and grain weight per plant, with a grain yield reduction of 82% and 30% when cultivated in greenhouse and field conditions, respectively. Such data on sowing period, night temperatures and the cold response of the rice cultivar used are important for the producer to consider.

Climate changes are expected to increase the severity of environmental adversities to plants, such as changes in rainfall regimes and the occurrence of more extreme temperatures, imposing a major risk to the productivity of agricultural crops. Throughout evolution, plants have evolved elegant mechanisms to cope with different adverse conditions, through the activation of different signaling pathways. The occurrence of abiotic stresses, such as osmotic stress or endoplasmic reticulum stress, tend to activate specific cellular pathways, such as the death cell signaling pathway mediated by proteins that contain DCD/NRP domains. The AtNRP1 and AtNRP2 proteins, components of the pathway in Arabidopsis, have been characterized as effectors of the programmed cell death process by the breakdown of the vacuolar membrane. Understanding how this pathway is integrated into cellular stability is essential, which justifies checking the predicted and not yet functionally characterized interactions among the components of the pathway with other proteins, such as AtCCR4a, a deadenylase that is both active in mRNA processing and in sucrose/starch metabolism. Given this context, we aimed to investigate the interaction between AtNRP2 and AtCCR4a, and its role during heat and drought stresses. We did not observe its direct involvement in the NRP-signaling pathway, however AtCCR4a was induced by osmotic and heat stresses. Furthermore, AtCCR4a disruption provides a drastically heat stress-sensitive phenotype, leading to reductions in photosynthetic pigment contents days after exposure to stress and negative changes in carbohydrate metabolism during this condition. Surprisingly, AtCCR4a disruption also promotes a more tolerant phenotype to water deficit, contributing to greater maintenance of relative water contents in leaf tissues and plant survival rate. These results indicate that AtCCR4a may have an antagonistic function in stress-responsive pathways, probably by regulating at a post-transcriptional level the expression of certain genes and/or by selecting specific target mRNAs. Keywords: Abiotic. Arabidopsis. Deadenylase. Heat. Water.