Irradiance level and elevation shape the soil microbiome communities of Coffea arabica L.

BACKGROUND: The nexus plant-microbe-environment is essential to understand the ecosystem processes shaping plant health and fitness. Within this triangle, soils and associated microflora are among the key ecosystem's drivers, underpinning plant productivity and evolution. In this study, we conducted a comprehensive analysis (physicochemical properties, enzyme activities, and taxonomic diversity) of soils under the canopy projection of Coffea arabica trees along a gradient of elevation (600, 800, and 900 m) and shade (0, 50, 100%). RESULTS: While shade had no influence on most parameters, altitude shaped the dynamics of microbial communities. Available phosphorus, soil organic carbon, and nitrate were significantly higher at 800 m, likely due to the higher activities of ß-glucosidase and phosphatases at this altitude. Microbial biomass (carbon and nitrogen) and moisture were significantly higher at 600 and 900 m, which might be attributed to the abundance and richness of soil microorganisms. Indeed, metabarcoding analysis revealed a complex pattern of microbial consortia (bacteria, archaea, fungi) at the three altitudes, with the lowest index of richness recorded at 800 m. The highest number of Amplicon Sequence Variants was observed in bacteria, whose functional analysis revealed distinct metabolic adaptations across different altitudes. At 900 m, the main functional attributes favored the responses to environmental stimuli and microbial interactions; at 800 m, the predominant metabolic pathways were related to organic matter, fermentation, and bioremediation; and at the lower 600 m, the pathways shifted towards the breakdown of plant-derived compounds (e.g. geraniol, limonene, and pinene degradation). CONCLUSION: Overall, the results indicate a higher effectiveness of the microbial consortium at 800 m, which might result in better nutrient cycling. The study highlights the importance of canopy shade species and elevation for the composition of microbial consortia in C. arabica, unveiling ecological functions beyond plant health, with implications for bio-based solutions and biotechnology.

Transcriptomic Analyses Reveal That Coffea arabica and Coffea canephora Have More Complex Responses under Combined Heat and Drought than under Individual Stressors.

Increasing exposure to unfavorable temperatures and water deficit imposes major constraints on most crops worldwide. Despite several studies regarding coffee responses to abiotic stresses, transcriptome modulation due to simultaneous stresses remains poorly understood. This study unravels transcriptomic responses under the combined action of drought and temperature in leaves from the two most traded species: Coffea canephora cv. Conilon Clone 153 (CL153) and C. arabica cv. Icatu. Substantial transcriptomic changes were found, especially in response to the combination of stresses that cannot be explained by an additive effect. A large number of genes were involved in stress responses, with photosynthesis and other physiologically related genes usually being negatively affected. In both genotypes, genes encoding for protective proteins, such as dehydrins and heat shock proteins, were positively regulated. Transcription factors (TFs), including MADS-box genes, were down-regulated, although responses were genotype-dependent. In contrast to Icatu, only a few drought- and heat-responsive DEGs were recorded in CL153, which also reacted more significantly in terms of the number of DEGs and enriched GO terms, suggesting a high ability to cope with stresses. This research provides novel insights into the molecular mechanisms underlying leaf Coffea responses to drought and heat, revealing their influence on gene expression.

Plant Responses to Climate Change.

Ongoing climate change poses a great risk to the natural environment and the sustainability of agriculture [...].

Genomic Evaluation of Coffea arabica and Its Wild Relative Coffea racemosa in Mozambique: Settling Resilience Keys for the Coffee Crop in the Context of Climate Change.

Climate change is negatively affecting the coffee value chain, with a direct effect on approximately 100 million people from 80 countries. This has been attributed to the high vulnerability of the two-mainstream species, Coffea arabica and Coffea canephora, to extreme weather events, with notable uneven increases in market prices. Taking into account the narrow genetic plasticity of the commercial coffee cultivars, wild-relatives and underutilized Coffea species are valuable genetic resources. In this work, we have assessed the occurrence of Coffea species in to understand the degree of genetic relationships between Coffea species in the country, as well as the patterns of genetic diversity, differentiation, and genetic structure. Only one wild species was found, C. racemosa, which showed a high level of genetic separation with C. arabica, based on plastid, as well as SSR and SNP analysis. C. arabica presented low levels of diversity likely related to their autogamous nature, while the allogamous C. racemosa presented higher levels of diversity and heterozygosity. The analysis of the functional pathways based on SNPs suggests that the stress signaling pathways are more robust in this species. This novel approach shows that it is vital to introduce more resilient species and increase genomic diversity in climate-smart practices.

Genetic and morphological diversity in populations of Annona senegalensis Pers. occurring in Western (Benin) and Southern (Mozambique) Africa.

Background: Understanding morpho-genetic diversity and differentiation of species with relatively large distributions is crucial for the conservation and sustainable management of their genetic resources. The present study focused on Annona senegalensis Pers., an important multipurpose wild plant, distributed exclusively in natural ecosystems but facing several threats. The study assessed the genetic and morphological diversity, structure, and differentiation of the species in populations from Western (Benin) and Southern (Mozambique) Africa. The material was evaluated to ascertain the environmental (climatic) determinants of the variation within this species. Methods: Four sub-populations comprised of 154 individuals were phenotyped based on nineteen plant, fruit, and leaf morphological traits and further genotyped using ten polymorphic nuclear microsatellite (nSSR) markers. Results: The results indicated strong differences in plant, fruit, and leaf morphological traits between Western and Southern populations. Furthermore, the studied populations were characterized by high genetic diversity, with an average genetic diversity index of 1.02. Western populations showed higher heterozygosity values (0.61-0.71) than Southern populations (0.41-0.49). Western and Southern populations were clearly differentiated into two different genetic groups, with further genetic subdivisions reflecting four sub-populations. Genetic variation between regions (populations) was higher (69.1%) than among (21.3%) and within (9.6%) sub-populations. Four distinct morphological clusters were obtained, which were strongly associated with the four genetic groups representing each sub-population. Climate, mainly precipitation and temperature indexes, explained the relatively higher variation found in morphological traits from Western (40.47%) in relation to Southern (27.98%) populations. Our study suggests that both environmental and genetic dynamics play an important role in the development of morphological variation in A. senegalensis.

The relative role of soil, climate, and genotype in the variation of nutritional value of Annona senegalensis fruits and leaves.

Annona senegalensis Pers is a multipurpose tree species valued for food and medicinal uses in Africa. Although there have been attempts to document the proximate composition of fruits and leaves, little is known about the relative role of soil, climate, and genotype on the nutritional quality. The present study evaluated the variation of the proximate composition of fruits and leaves in populations from Benin and Mozambique. It further assessed the impact of soil, climate and genotype on the proximate composition. Data were collected from four populations genetically different and analyzed using descriptive statistics, analysis of variance (ANOVA), principal component analysis, redundancy analysis (RDA), and variance partitioning. Results revealed significant variation in the proximate composition of fruits and leaves among the studied populations. Ashes and fibers in fruits, and lipids in leaves were 4.8-fold, 2.5- fold, and 1.25-fold higher respectively, in populations from Mozambique. Fruits moisture and lipids content were rather 1.4-fold and 1.10-fold higher in populations from Benin. Moisture and lipids were respectively 6-fold and 1.27-fold higher in fruits than in leaves, while ashes, fibers and proteins were approximately twice higher in the leaves than in the fruits. Genetic groups, climate and soils were found to influence this variation. All three factors explained 74.4% of the variation of nutritional value of fruits and leaves, 31.9% of which was exclusively due to genetic variation, 2.8% to the interaction of climate and soils, 24.1% to the interaction of soil and genetic variation, and 15.5% to the interaction of all three factors. Our study shows that genetic variation and soil properties better than climate, explain the variation of nutritional value of A. senegalensis fruits and leaves and further provides essential information that could be harnessed in the domestication and breeding program of the species for its edible parts.

Overexpression of Water-Responsive Genes Promoted by Elevated CO2 Reduces ROS and Enhances Drought Tolerance in Coffea Species.

Drought is a major constraint to plant growth and productivity worldwide and will aggravate as water availability becomes scarcer. Although elevated air [CO2] might mitigate some of these effects in plants, the mechanisms underlying the involved responses are poorly understood in woody economically important crops such as Coffea. This study analyzed transcriptome changes in Coffea canephora cv. CL153 and C. arabica cv. Icatu exposed to moderate (MWD) or severe water deficits (SWD) and grown under ambient (aCO2) or elevated (eCO2) air [CO2]. We found that changes in expression levels and regulatory pathways were barely affected by MWD, while the SWD condition led to a down-regulation of most differentially expressed genes (DEGs). eCO2 attenuated the impacts of drought in the transcripts of both genotypes but mostly in Icatu, in agreement with physiological and metabolic studies. A predominance of protective and reactive oxygen species (ROS)-scavenging-related genes, directly or indirectly associated with ABA signaling pathways, was found in Coffea responses, including genes involved in water deprivation and desiccation, such as protein phosphatases in Icatu, and aspartic proteases and dehydrins in CL153, whose expression was validated by qRT-PCR. The existence of a complex post-transcriptional regulatory mechanism appears to occur in Coffea explaining some apparent discrepancies between transcriptomic, proteomic, and physiological data in these genotypes.

Uncovering the wide protective responses in Coffea spp. leaves to single and superimposed exposure of warming and severe water deficit.

Climate changes boosted the frequency and severity of drought and heat events, with aggravated when these stresses occur simultaneously, turning crucial to unveil the plant response mechanisms to such harsh conditions. Therefore, plant responses/resilience to single and combined exposure to severe water deficit (SWD) and heat were assessed in two cultivars of the main coffee-producing species: Coffea arabica cv. Icatu and C. canephora cv. Conilon Clone 153 (CL153). Well-watered plants (WW) were exposed to SWD under an adequate temperature of 25/20°C (day/night), and thereafter submitted to a gradual increase up to 42/30°C, and a 14-d recovery period (Rec14). Greater protective response was found to single SWD than to single 37/28°C and/or 42/30°C (except for HSP70) in both cultivars, but CL153-SWD plants showed the larger variations of leaf thermal imaging crop water stress index (CWSI, 85% rise at 37/28°C) and stomatal conductance index (IG, 66% decline at 25/20°C). Both cultivars revealed great resilience to SWD and/or 37/28°C, but a tolerance limit was surpassed at 42/30°C. Under stress combination, Icatu usually displayed lower impacts on membrane permeability, and PSII function, likely associated with various responses, usually mostly driven by drought (but often kept or even strengthened under SWD and 42/30°C). These included the photoprotective zeaxanthin and lutein, antioxidant enzymes (superoxide dismutase, Cu,Zn-SOD; ascorbate peroxidase, APX), HSP70, arabinose and mannitol (involving de novo sugar synthesis), contributing to constrain lipoperoxidation. Also, only Icatu showed a strong reinforcement of glutathione reductase activity under stress combination. In general, the activities of antioxidative enzymes declined at 42/30°C (except Cu,Zn-SOD in Icatu and CAT in CL153), but HSP70 and raffinose were maintained higher in Icatu, whereas mannitol and arabinose markedly increased in CL153. Overall, a great leaf plasticity was found, especially in Icatu that revealed greater responsiveness of coordinated protection under all experimental conditions, justifying low PIChr and absence of lipoperoxidation increase at 42/30°C. Despite a clear recovery by Rec14, some aftereffects persisted especially in SWD plants (e.g., membranes), relevant in terms of repeated stress exposure and full plant recovery to stresses.

Salt Stress Tolerance in Casuarina glauca: Insights from the Branchlets Transcriptome.

Climate change and the accelerated rate of population growth are imposing a progressive degradation of natural ecosystems worldwide. In this context, the use of pioneer trees represents a powerful approach to reverse the situation. Among others, N2-fixing actinorhizal trees constitute important elements of plant communities and have been successfully used in land reclamation at a global scale. In this study, we have analyzed the transcriptome of the photosynthetic organs of Casuarina glauca (branchlets) to unravel the molecular mechanisms underlying salt stress tolerance. For that, C. glauca plants supplied either with chemical nitrogen (KNO3+) or nodulated by Frankia (NOD+) were exposed to a gradient of salt concentrations (200, 400, and 600 mM NaCl) and RNA-Seq was performed. An average of ca. 25 million clean reads was obtained for each group of plants, corresponding to 86,202 unigenes. The patterns of differentially expressed genes (DEGs) clearly separate two groups: (i) control- and 200 mM NaCl-treated plants, and (ii) 400 and 600 mM NaCl-treated plants. Additionally, although the number of total transcripts was relatively high in both plant groups, the percentage of significant DEGs was very low, ranging from 6 (200 mM NaCl/NOD+) to 314 (600 mM NaCl/KNO3+), mostly involving down-regulation. The vast majority of up-regulated genes was related to regulatory processes, reinforcing the hypothesis that some ecotypes of C. glauca have a strong stress-responsive system with an extensive set of constitutive defense mechanisms, complemented by a tight mechanism of transcriptional and post-transcriptional regulation. The results suggest that the robustness of the stress response system in C. glauca is regulated by a limited number of genes that tightly regulate detoxification and protein/enzyme stability, highlighting the complexity of the molecular interactions leading to salinity tolerance in this species.

Protective Responses at the Biochemical and Molecular Level Differ between a Coffea arabica L. Hybrid and Its Parental Genotypes to Supra-Optimal Temperatures and Elevated Air [CO2].

Climate changes with global warming associated with rising atmospheric [CO2] can strongly impact crop performance, including coffee, which is one of the most world's traded agricultural commodities. Therefore, it is of utmost importance to understand the mechanisms of heat tolerance and the potential role of elevated air CO2 (eCO2) in the coffee plant response, particularly regarding the antioxidant and other protective mechanisms, which are crucial for coffee plant acclimation. For that, plants of Coffea arabica cv. Geisha 3, cv. Marsellesa and their hybrid (Geisha 3 × Marsellesa) were grown for 2 years at 25/20 °C (day/night), under 400 (ambient CO2, aCO2) or 700 µL (elevated CO2, eCO2) CO2 L-1, and then gradually submitted to a temperature increase up to 42/30 °C, followed by recovery periods of 4 (Rec4) and 14 days (Rec14). Heat (37/28 °C and/or 42/30 °C) was the major driver of the response of the studied protective molecules and associated genes in all genotypes. That was the case for carotenoids (mostly neoxanthin and lutein), but the maximal (α + ß) carotenes pool was found at 37/28 °C only in Marsellesa. All genes (except VDE) encoding for antioxidative enzymes (catalase, CAT; superoxide dismutases, CuSODs; ascorbate peroxidases, APX) or other protective proteins (HSP70, ELIP, Chape20, Chape60) were strongly up-regulated at 37/28 °C, and, especially, at 42/30 °C, in all genotypes, but with maximal transcription in Hybrid plants. Accordingly, heat greatly stimulated the activity of APX and CAT (all genotypes) and glutathione reductase (Geisha3, Hybrid) but not of SOD. Notably, CAT activity increased even at 42/30 °C, concomitantly with a strongly declined APX activity. Therefore, increased thermotolerance might arise through the reinforcement of some ROS-scavenging enzymes and other protective molecules (HSP70, ELIP, Chape20, Chape60). Plants showed low responsiveness to single eCO2 under unstressed conditions, while heat promoted changes in aCO2 plants. Only eCO2 Marsellesa plants showed greater contents of lutein, the pool of the xanthophyll cycle components (V + A + Z), and ß-carotene, compared to aCO2 plants at 42/30 °C. This, together with a lower CAT activity, suggests a lower presence of H2O2, likely also associated with the higher photochemical use of energy under eCO2. An incomplete heat stress recovery seemed evident, especially in aCO2 plants, as judged by the maintenance of the greater expression of all genes in all genotypes and increased levels of zeaxanthin (Marsellesa and Hybrid) relative to their initial controls. Altogether, heat was the main response driver of the addressed protective molecules and genes, whereas eCO2 usually attenuated the heat response and promoted a better recovery. Hybrid plants showed stronger gene expression responses, especially at the highest temperature, when compared to their parental genotypes, but altogether, Marsellesa showed a greater acclimation potential. The reinforcement of antioxidative and other protective molecules are, therefore, useful biomarkers to be included in breeding and selection programs to obtain coffee genotypes to thrive under global warming conditions, thus contributing to improved crop sustainability.

High-resolution shotgun proteomics reveals that increased air [CO2] amplifies the acclimation response of coffea species to drought regarding antioxidative, energy, sugar, and lipid dynamics.

As drought threatens crop productivity it is crucial to characterize the defense mechanisms against water deficit and unveil their interaction with the expected rise in the air [CO2]. For that, plants of Coffea canephora cv. Conilon Clone 153 (CL153) and C. arabica cv. Icatu grown under 380 (aCO2) or 700 µL L-1 (eCO2) were exposed to moderate (MWD) and severe (SWD) water deficits. Responses were characterized through the activity and/or abundance of a selected set of proteins associated with antioxidative (e.g., Violaxanthin de-epoxidase, Superoxide dismutase, Ascorbate peroxidases, Monodehydroascorbate reductase), energy/sugar (e.g., Ferredoxin-NADP reductase, NADP-dependent glyceraldehyde-3-phosphate dehydrogenase, sucrose synthase, mannose-6-phosphate isomerase, Enolase), and lipid (Lineolate 13S-lipoxygenase) processes, as well as with other antioxidative (ascorbate) and protective (HSP70) molecules. MWD caused small changes in both genotypes regardless of [CO2] level while under the single imposition to SWD, only Icatu showed a global reinforcement of most studied proteins supporting its tolerance to drought. eCO2 alone did not promote remarkable changes but strengthened a robust multi-response under SWD, even supporting the reversion of impacts already observed by CL153 at aCO2. In the context of climate changes where water constraints and [CO2] levels are expected to increase, these results highlight why eCO2 might have an important role in improving drought tolerance in Coffea species.

Editorial: Tropical Plant Responses to Climate Change.

The climate crisis is pushing the planet's tropical plants towards their limits [...].

Food and medicinal uses of Annona senegalensis Pers.: a country-wide assessment of traditional theoretical knowledge and actual uses in Benin, West Africa.

BACKGROUND: The growing interest for more natural products in food and health industries has led to increasing research on traditional knowledge related to plants. While theoretical knowledge (TK) on the uses of a species informs on the wide spectrum of potential uses of that species, actual uses (AU) highlight their potential being actually used. Distinguishing between the two is important when reporting ethnobotanical studies. However, studies often equated AU and TK, sometimes misleading conclusions, and decision-making. This study assessed TK, AU, and difference between TK and AU of Annona senegalensis and how each is related to factors such as age, sex, sociolinguistic group, and main activity in Benin republic. METHODS: Data were collected through semi-structured individual interviews (n = 755) and analyzed using among others, relative frequency of citation (RFC), and use-value (UV). RESULTS: A total of 168 theoretical uses were recorded but only 92 were "actually" practiced, of which four were food and 88 medicinal uses. TK and AU were positively correlated. As expected, TK was also significantly higher than AU, indicating that some potential uses of the species are still not valued. Sociolinguistic group and main activity, not age and sex, were the main factors influencing TK, AU, and difference between TK and AU. The highest TK was found with Bariba sociolinguistic group and the highest AU with Otamari. Fruits (100%) and flowers (10%) were the most used organs for food, while leaves (40%) and roots (7%) were mostly used for medicinal purposes. The most common food uses were consumption of the ripe fruits (100%), and food seasoning with flowers (10%). The most cited diseases were malaria (28%) and intestinal worms (8%). CONCLUSIONS: The study illustrated the importance of differentiating between TK and AU. It documented  the wide range of the uses of A. senegalensis, while highlighting its most common uses, and the need to better valorize and sustainably manage the species.

Will Casuarina glauca Stress Resilience Be Maintained in the Face of Climate Change?

Actinorhizal plants have been regarded as promising species in the current climate change context due to their high tolerance to a multitude of abiotic stresses. While combined salt-heat stress effects have been studied in crop species, their impact on the model actinorhizal plant, Casuarina glauca, has not yet been fully addressed. The effect of single salt (400 mM NaCl) and heat (control at 26/22 °C, supra optimal temperatures at 35/22 °C and 45/22 °C day/night) conditions on C. glauca branchlets was characterised at the physiological level, and stress-induced metabolite changes were characterised by mass spectrometry-based metabolomics. C. glauca could withstand single salt and heat conditions. However, the harshest stress condition (400 mM NaCl, 45 °C) revealed photosynthetic impairments due to mesophyll and membrane permeability limitations as well as major stress-specific differential responses in C and N metabolism. The increased activity of enzymatic ROS scavengers was, however, revealed to be sufficient to control the plant oxidative status. Although C. glauca could tolerate single salt and heat stresses, their negative interaction enhanced the effects of salt stress. Results demonstrated that C. glauca responses to combined salt-heat stress could be explained as a sum of the responses from each single applied stress.

The Nexus between Fire and Soil Bacterial Diversity in the African Miombo Woodlands of Niassa Special Reserve, Mozambique.

(1) Background: the Miombo woodlands comprise the most important vegetation from southern Africa and are dominated by tree legumes with an ecology highly driven by fires. Here, we report on the characterization of bacterial communities from the rhizosphere of Brachystegia boehmii in different soil types from areas subjected to different regimes. (2) Methods: bacterial communities were identified through Illumina MiSeq sequencing (16S rRNA). Vigna unguiculata was used as a trap to capture nitrogen-fixing bacteria and culture-dependent methods in selective media were used to isolate plant growth promoting bacteria (PGPB). PGP traits were analysed and molecular taxonomy of the purified isolates was performed. (3) Results: Bacterial communities in the Miombo rhizosphere are highly diverse and driven by soil type and fire regime. Independent of the soil or fire regime, the functional diversity was high, and the different consortia maintained the general functions. A diverse pool of diazotrophs was isolated, and included symbiotic (e.g., Mesorhizobium sp., Neorhizobium galegae, Rhizobium sp., and Ensifer adhaerens), and non-symbiotic (e.g., Agrobacterium sp., Burkholderia sp., Cohnella sp., Microvirga sp., Pseudomonas sp., and Stenotrophomonas sp.) bacteria. Several isolates presented cumulative PGP traits. (4) Conclusions: Although the dynamics of bacterial communities from the Miombo rhizosphere is driven by fire, the maintenance of high levels of diversity and functions remain unchanged, constituting a source of promising bacteria in terms of plant-beneficial activities such as mobilization and acquisition of nutrients, mitigation of abiotic stress, and modulation of plant hormone levels.

Primary Metabolite Profile Changes in Coffea spp. Promoted by Single and Combined Exposure to Drought and Elevated CO2 Concentration.

Climate change scenarios pose major threats to many crops worldwide, including coffee. We explored the primary metabolite responses in two Coffea genotypes, C. canephora cv. Conilon Clone 153 and C. arabica cv. Icatu, grown at normal (aCO2) or elevated (eCO2) CO2 concentrations of 380 or 700 ppm, respectively, under well-watered (WW), moderate (MWD), or severe (SWD) water deficit conditions, in order to assess coffee responses to drought and how eCO2 can influence such responses. Primary metabolites were analyzed with a gas chromatography time-of-flight mass spectrometry metabolomics platform (GC-TOF-MS). A total of 48 primary metabolites were identified in both genotypes (23 amino acids and derivatives, 10 organic acids, 11 sugars, and 4 other metabolites), with differences recorded in both genotypes. Increased metabolite levels were observed in CL153 plants under single and combined conditions of aCO2 and drought (MWD and SWD), as opposed to the observed decreased levels under eCO2 in both drought conditions. In contrast, Icatu showed minor differences under MWD, and increased levels (especially amino acids) only under SWD at both CO2 concentration conditions, although with a tendency towards greater increases under eCO2. Altogether, CL153 demonstrated large impact under MWD, and seemed not to benefit from eCO2 in either MWD and SWD, in contrast with Icatu.

Exploring physicochemical and cytogenomic diversity of African cowpea and common bean.

In sub-Saharan Africa, grain legumes (pulses) are essential food sources and play an important role in sustainable agriculture. Among the major pulse crops, the native cowpea (Vigna unguiculata) and introduced common bean (Phaseolus vulgaris) stand out. This paper has two main goals. First, we provide a comprehensive view of the available genetic resources of these genera in Africa, including data on germplasm collections and mapping biodiversity-rich areas. Second, we investigate patterns of physicochemical and cytogenomic variation across Africa to explore the geographical structuring of variation between native and introduced beans. Our results revealed that 73 Vigna and 5 Phaseolus species occur in tropical regions of Africa, with 8 countries accounting for more than 20 native species. Conversely, germplasm collections are poorly represented when compared to the worldwide collections. Regarding the nuclear DNA content, on average, V. unguiculata presents significantly higher values than P. vulgaris. Also, V. unguiculata is enriched in B, Mg, S, and Zn, while P. vulgaris has more Fe, Ca, and Cu. Overall, our study suggests that the physicochemical and cytogenomic diversity of native Vigna species is higher than previously thought, representing valuable food resources to reduce food insecurity and hunger, particularly of people living in African developing countries.

Iron Biofortification in Rice: An Update on Quantitative Trait Loci and Candidate Genes.

Rice is the most versatile model for cereals and also an economically relevant food crop; as a result, it is the most suitable species for molecular characterization of Fe homeostasis and biofortification. Recently there have been significant efforts to dissect genes and quantitative trait loci (QTL) associated with Fe translocation into rice grains; such information is highly useful for Fe biofortification of cereals but very limited in other species, such as maize (Zea mays) and wheat (Triticum aestivum). Given rice's centrality as a model for Poaceae species, we review the current knowledge on genes playing important roles in Fe transport, accumulation, and distribution in rice grains and QTLs that might explain the variability in Fe concentrations observed in different genotypes. More than 90 Fe QTLs have been identified over the 12 rice chromosomes. From these, 17 were recorded as stable, and 25 harbored Fe-related genes nearby or within the QTL. Among the candidate genes associated with Fe uptake, translocation, and loading into rice grains, we highlight the function of transporters from the YSL and ZIP families; transporters from metal-binding molecules, such as nicotianamine and deoxymugineic acid; vacuolar iron transporters; citrate efflux transporters; and others that were shown to play a role in steps leading to Fe delivery to seeds. Finally, we discuss the application of these QTLs and genes in genomics assisted breeding for fast-tracking Fe biofortification in rice and other cereals in the near future.