Functional Analysis of the Genotypic Differences in Response of Pea (Pisum sativum L.) to Calcareous-Induced Iron Deficiency

Lime-induced iron chlorosis is a major nutritional disorder causing severe plant growth and yield reduction in the calcareous soils of Tunisia.The understanding the behavior of key metabolic functions of peas on calcareous soils,the identification of useful traits of tolerance,and the exploration of the genotypic differences in response to this constraint remain the most efficient approaches due to their coast,environmental benefits,and sustainability.For this purpose,a greenhouse experiment was conducted on three pea genotypes(Alexandra:Alex,Douce de provence:DP,and Merveille de Kelvedon:MK)cultivated on calcareous soil(Fe-deficient)and fertile soil(control).Plant growth,SPAD index,iron nutrition and distribution,photosynthesis,and antioxidant enzymes were deeply analyzed to discriminate genotypic differences.Calcareous-induced iron deficiency reduced SPAD index,plant growth,net photosynthesis,and tissue Fe content against a significant stimulation of the oxidative stress indicators,H2O2 and Malondialdehyde(MDA).Moreover,we reported a significant induction of SOD and CAT activity in shoots and roots of the Alexandra genotype.Fe use efficiency increased on calcareous soil and clearly discriminated the studied genotypes.Alexandra genotype was found to be the most tolerant to lime-induced iron chlorosis.This genotype protects its tissues against oxidative stress by stimulating enzyme activities(SOD and CAT)and develops significant efficiency of Fe uptake,translocation to shoots and use when cultivated on calcareous soil.

Secretion of Phy tosiderophore and Its Effects on Soil Fe Availability

Large amounts of phytosiderophore are detected from both the solution and the rhizosphere soil when cereal crops are under Fe deficiency stress. The extension of phytosiderophore in the rhizosphere soil is found only within 1 mm apart from the root surface. The rate of phytosiderophore secretion is negatively related to chlorophyll content in young leaves and positively related to the Fe-solubilizing capacity. Results from in vitro experiments show 10 μmoles mugineic acid can dissolve 501 μg Fe from iron hydroxide and 146 ug from strengite. Thus, phytosiderophore can considerably enhance the soil iron availability by increasing the solubility of amorphous iron hydroxide and iron phosphate, and active Fe is consequently accumulated in the plant rhizosphere , 43% higher than in the bulk soils. There is evidence to support that mugineic acid chelates with Fe3+at a rate of 1:1 in the acid condition. In addition ,we observe mugineic acid has certain effects on mobilization of P as well as Fe by dissolving the insoluble iron phosphate. And phytosiderophore seems to be an effective remedy for the chlorosis of dicotyledonous plants.

Iron Deficiency-induced Increase of Root Branching Contributes to the Enhanced Root Ferric Chelate Reductase Activity

In various plant species, Fe deficiency increases lateral root branching. However, whether this morphological alteration contributes to the Fe deficiency-induced physiological responses still remains to be demonstrated. In the present research, we demonstrated that the lateral root development of red clover （Trifolium pretense L.） was significantly enhanced by Fe deficient treatment, and the total lateral root number correlated well with the Fe deficiency-induced ferric chelate reductase （FCR） activity. By analyzing the results from Dasgan et al. （2002）, we also found that although the two tomato genotypes line227/1 （P1） and Roza （P2） and their reciprocal F1 hybrid lines （＂P1 × P2＂ and ＂P2 ×PI＂） were cultured under two different lower Fe conditions （10^-6 and 10^-7 M FeEDDHA）, their FCR activities are significantly correlated with the lateral root number. More interestingly, the -Fe chlorosis tolerant ability of these four tomato lines displays similar trends with the lateral root density. Taking these results together, it was proposed that the Fe deficiency-induced increases of the lateral root should play an important role in resistance to Fe deficiency, which may act as harnesses of a useful trait for the selection and breeding of more Fe-efficient crops among the genotypes that have evolved a Fe deficiency-induced Fe uptake system.

The miR157-SPL-CNR module acts upstream of bHLH101 to negatively regulate iron deficiency responses in tomato

Iron(Fe)homeostasis is critical for plant growth,development,and stress responses.Fe levels are tightly controlled by intricate regulatory networks in which transcription factors(TFs)play a central role.A series of basic helix-loop-helix(b HLH)TFs have been shown to contribute to Fe homeostasis,but the regulatory layers beyond b HLH TFs remain largely unclear.Here,we demonstrate that the SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE(SPL)TF Sl SPL-CNR negatively regulates Fe-deficiency responses in tomato(Solanum lycopersicum)roots.Fe deficiency rapidly repressed the expression of Sl SPL-CNR,and Fe deficiency responses were intensified in two clustered regularly interspaced palindromic repeats(CRISPR)/CRISPRassociated protein 9-generated Sl SPL-CNR knockout lines compared to the wild-type.Comparative transcriptome analysis identified 47 Fe deficiencyresponsive genes the expression of which is negatively regulated by Sl SPL-CNR,one of which,Slb HLH101,helps regulate Fe uptake genes.Sl SPLCNR localizes the nucleus and interacts with the GTAC and BOX 4(ATTAAT)motifs in the Slb HLH101 promoter to repress its expression.Inhibition of Sl SPL-CNR expression in response to Fe deficiency was well correlated with the expression of the micro RNA Slymi R157.Slymi R157-overexpressing tomato lines displayed enhanced Fe deficiency responses,as did Sl SPL-CNR loss-of-function mutants.We propose that the Slymi R157-Sl SPL-CNR module represents a novel pathway that acts upstream of Slb HLH101 to regulate Fe homeostasis in tomato roots.

Siderophore-Producing Rhizobacteria as a Promising Tool for Empowering Plants to Cope with Iron Limitation in Saline Soils:A Review

Iron(Fe) bioavailability to plants is reduced in saline soils;however, the exact mechanisms underlying this effect are not yet completely understood. Siderophore-expressing rhizobacteria may represent a promising alternative to chemical fertilizers by simultaneously tackling salt-stress effects and Fe limitation in saline soils. In addition to draught, plants growing in arid soils face two other major challenges: high salinity and Fe deficiency. Salinity attenuates growth, affects plant physiology, and causes nutrient imbalance,which is, in fact, one of the major consequences of saline stress. Iron is a micronutrient essential for plant development, and it is required by several metalloenzymes involved in photosynthesis and respiration. Iron deficiency is associated with chlorosis and low crop productivity. The role of microbial siderophores in Fe supply to plants and the effect of plant growth-promoting rhizobacteria(PGPR) on the mitigation of saline stress in crop culture are well documented. However, the dual effect of siderophore-producing PGPR, both on salt stress and Fe limitation, is still poorly explored. This review provides a critical overview of the combined effects of Fe limitation and soil salinization as challenges to modern agriculture and intends to summarize some indirect evidence that argues in favour of siderophore-producing PGPR as biofertilization agents in salinized soils. Recent developments and future perspectives on the use of PGPR are discussed as clues to sustainable agricultural practices in the context of present and future climate change scenarios.