Orthophosphate (H2PO4  −, Pi) is an essential macronutrient required for many fundamental processes in plants, including photosynthesis and respiration, as well as nucleic acid, protein, and membrane phospholipid synthesis. The immense use of Pi-containing fertilizers in agriculture demonstrates how the soluble Pi levels of most soils are suboptimal for crop growth. The aim of this review is to explore recent and exciting advances concerning our understanding of adaptive metabolic processes that plants have evolved to alleviate the negative impact of nutritional Pi deficiency. Plant Pi starvation responses arise from complex signaling pathways that integrate altered gene expression with post-transcriptional and post-translational mechanisms. The resultant remodeling of the transcriptome, proteome, and metabolome enhances the efficiency of root Pi acquisition from the soil, as well as the use of assimilated Pi throughout the plant. We emphasize how the upregulation of high affinity Pi transporters and intra- and extracellular Pi scavenging and recycling enzymes, organic acid anion efflux, membrane remodeling, and the remarkable flexibility of plant metabolism and bioenergetics contribute to the survival of Pi-deficient plants. This research field is enabling development of a broad range of innovative and promising strategies for engineering P-efficient crops. Such cultivars are urgently needed to reduce inputs of unsustainable and nonrenewable Pi fertilizers for maximum agronomic benefit, and long-term global food security and ecosystem preservation.

Orthophosphate (H PO , Pi) is an essential macronutrient integral to energy metabolism as well as a component of membrane lipids, nucleic acids, including ribosomal RNA, and therefore essential for protein synthesis. The Pi concentration in the solution of most soils worldwide is usually far too low for maximum growth of crops, including rice. This has prompted the massive use of inefficient, polluting, and nonrenewable phosphorus (P) fertilizers in agriculture. We urgently need alternative and more sustainable approaches to decrease agriculture's dependence on Pi fertilizers. These include manipulating crops by (a) enhancing the ability of their roots to acquire limiting Pi from the soil (i.e. increased P-acquisition efficiency) and/or (b) increasing the total biomass/yield produced per molecule of Pi acquired from the soil (i.e. increased P-use efficiency). Improved P-use efficiency may be achieved by producing high-yielding plants with lower P concentrations or by improving the remobilization of acquired P within the plant so as to maximize growth and biomass allocation to developing organs. Membrane lipid remodelling coupled with hydrolysis of RNA and smaller P-esters in senescing organs fuels P remobilization in rice, the world's most important cereal crop.

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SUMMARYThe capability of some plant species to mobilize phosphorus (P) from poorly available soil P fractions can improve P availability for P-inefficient plant species in intercropping. White lupin (Lupinus albus) has been investigated as a model P-mobilizing plant for its capability of enhancing the P acquisition of neighbouring species under P-limited conditions. To date, investigations have led to contrasting findings, where some reports have described a positive effect of intercropped lupins on companion plants, whereas others have revealed no effects. This review summarizes the literature related to lupin–cereal intercropping. It explores the underpinning mechanisms that influence interspecific facilitation of P acquisition. The P-mobilization-based facilitation by lupins to enhance P-acquisition of co-occurring plant species is determined by both available P concentration and P-sorption capacity of soil, and the root intermingling capacity among two plant partners enabling rhizosphere overlapping. In lupin–cereal intercropping, lupin enhances the below-ground concentration of labile P pools through mobilization of P from sparingly available P pools, which is accomplished through carboxylate exudation, where neighbouring species acquire part of the mobilized P. The non-P-mobilizing species benefit only under P-limited conditions when they immediately occupy the maximum soil volume influenced by P-mobilizing lupin. Positive effects of mixed cropping are apparent in alkaline, neutral and acidic soils. However, the facilitation of P acquisition by lupins to companion species is eliminated when soil becomes strongly P-sorbing. In such soils, the limitation of root growth can result in poorer root intermingling between two species. The P mobilized by lupins might not be acquired by neighbouring species because it is bound to P-sorbing compounds. We suggest that the lupins can be best used as P-mobilizing plant species to enhance P acquisition of P-inefficient species under P-limited conditions when plant species are grown with compatible crops and soil types that facilitate sharing of rhizosphere functions among intercropped partners.

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Phosphorus (P) is a major nutrient supporting rice productivity. Improving low-P tolerance of rice is expected to reduce dependence on P fertilizer, thereby reducing rice production costs and environmental impacts. This report describes the mapping of quantitative trait loci (QTL) associated with P deficiency tolerance in japonica rice. An F5 population derived from a cross of the low-P tolerant cultivar Akamai (Yamagata) and the sensitive cultivar Koshihikari was evaluated for shoot growth under low-P conditions. Then single nucleotide polymorphism (SNP) profiles of the low-P tolerant and sensitive bulks were compared on a genome-wide scale by QTL-Seq, a rapid QTL mapping method using next-generation sequencing technology. Results show a major QTL associated with low-P tolerance located on the long arm of chromosome 12. It has been named QTL for low-P tolerance 1 or qLPT1. SNPs were detected in 45 genes of qLPT1 region and the 5 genes were harboring synonymous SNPs, although none of them had been reported as involved in low-P tolerance. This result implies that the novel gene responsible for low-P tolerance exists in qLPT1. This study will contribute to the elucidation of mechanisms underlying low-P tolerance of Akamai and will facilitate the breeding of rice with low-P tolerance.

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