Abstract Intracellular inorganic orthophosphate (Pi) distribution and homeostasis profoundly affect plant growth and development. However, its distribution patterns remain elusive owing to the lack of efficient cellular Pi imaging methods. Here we develop a rapid colorimetric Pi imaging method, inorganic orthophosphate staining assay (IOSA), that can semi-quantitatively image intracellular Pi with high resolution. We used IOSA to reveal the alteration of cellular Pi distribution caused by Pi starvation or mutations that alter Pi homeostasis in two model plants, rice and Arabidopsis, and found that xylem parenchyma cells and basal node sieve tube element cells play a critical role in Pi homeostasis in rice.
Abstract Inorganic phosphate (Pi) availability is an important factor that affects the growth and yield of crops, thus an appropriate and effective response to Pi-fluctuation is critical. However, how crops orchestrate Pi-signaling and growth under Pi-starvation conditions to optimize the growth defense tradeoff remains unclear. Here we show that a Pi-starvation induced transcription factor NIGT1 (NITRATE-INDUCIBLE GARP-TYPE TRANSCRIPTIONAL REPRESSOR 1) controls plant growth and prevents a hyperresponse to Pi-starvation by directly repressing the expression of growth-related and Pi-signaling genes to achieve a balance between growth and response under a varying Pi environment.
Abstract As a finite and non-renewable resource, phosphorus (P) is essential to all life and crucial for crop growth and food production. The boosted agricultural use and associated loss of P to the aquatic environment are increasing environmental pollution, harming ecosystems, and threatening future global food security. Thus, recovering and reusing P from water bodies is urgently needed to close the P cycle. As a natural, eco-friendly, and sustainable reclamation strategy, microalgae-based biological P recovery is considered a promising solution.
Abstract The basal levels of salicylic acid (SA) vary dramatically among plant species. In the shoot, for example, rice contains almost 100 times higher SA levels than Arabidopsis. Despite its high basal levels, neither the biosynthetic pathway nor the biological functions of SA are well understood in rice.
Combining with metabolites analysis, physiological, and genetic approaches, we found that the synthesis of basal SA in rice shoot is dependent on OsAIM1, which encodes a beta-oxidation enzyme in the phenylalanine ammonia-lyase (PAL) pathway.
Abstract Phosphate (Pi) is involved in numerous metabolic processes and plays a vital role in plant growth. Green plants have evolved intricate molecular bases of Pi-signaling to maintain cellular Pi homeostasis. Here, we summarize recent advances in the molecular and structural bases of central Pi-signaling and discuss pending questions.
Discovery of the core elements involved in P signaling
(A) Key studies uncovering the molecular and structural basis of P signaling machines.
Abstract Salicylic acid (SA) plays a pivotal role in plant response to biotic and abiotic stress. Several core SA signaling regulators and key proteins in SA biosynthesis have been well charactered. However, much remains unknown about the origin, evolution, and early diversification of core elements in plant SA signaling and biosynthesis. Here, we identified ten core protein families in SA signaling and biosynthesis across green plant lineages. We found that key SA signaling receptors, the nonexpresser of pathogenesis-related proteins (NPRs), originated in the most recent common ancestor (MRCA) of land plants and formed divergent groups in the ancestor of seed plants.
Abstract Phosphate (Pi) limitation represents a primary constraint on crop production. To better cope with Pi deficiency stress, plants have evolved multiple adaptive mechanisms for phosphorus acquisition and utilization, including the alteration of growth and the activation of Pi starvation signaling. However, how these strategies are coordinated remains largely unknown. Here, we found that the alternative splicing (AS) of REGULATOR OF LEAF INCLINATION 1 (RLI1) in rice (Oryza sativa) produces two protein isoforms: RLI1a, containing MYB DNA binding domain; and RLI1b, containing both MYB and coiled-coil (CC) domains.
Summary Phosphorous (P) and iron (Fe) are two essential nutrients for plant growth and development and are highly abundant elements in the earth’s crust but often display low availability to plants. Due to the ability to form insoluble complexes, the antagonistic interaction between P and Fe nutrition in plants has been noticed for decades. However, the underlying molecular mechanism modulating the signaling and homeostasis between them is still obscure. Here, we show that the possible iron sensors HRZs, iron deficiency induced E3 ligases, could interact with the central regulator for phosphate (Pi) signaling, PHR2, and prompt its ubiquitination at lysine residues K319 and K328, leading to its degradation in rice.
Summary Phosphorus (P) is an essential element for plant growth and development. Vacuoles play a fundamental role in the storage and remobilization of P in plants, while our understanding of the evolutionary mechanisms of creating and reusing P stores are limited. Besides, we also know very little about the coordination of intercellular P translocation, neither the inorganic phosphate (Pi) signaling nor the Pi transport patterns. Here we summarize recent advances in understanding the core elements involved in cellular and/or subcellular P homeostasis and signaling in unicellular green algae and multicellular land plants.
OsPHO1;2 exports excess Pi from endosperm to maintain proper levels of AGPase activity for starch biosynthesis
During starch biosynthesis in developing endosperm, glucose-1-P and ATP are converted into ADP-glucose and inorganic pyrophosphate (PPi) by ADP-glucose pyrophosphorylase (AGPase). ADP-glucose is used for starch biosynthesis and PPi is hydrolyzed into Pi. The plasma membrane (PM)-localized OsPHO1;2 is expressed in the endosperm cells and exports excess Pi from the developing endosperm to maintain Pi homeostasis for proper levels of AGPase activity and starch biosynthesis.
Summary Both genetic and epigenetic information must be transferred from mother to daughter cells during cell division. The mechanisms through which information about chromatin states and epigenetic marks like histone 3 lysine 27 trimethylation (H3K27me3) are transferred have been characterized in animals; these processes are less well understood in plants. Here, based on characterization of a dwarf rice (Oryza sativa) mutant (dwarf-related wd40 protein 1, drw1) deficient for yeast CTF4 (CHROMOSOME TRANSMISSION FIDELITY PROTEIN 4), we discovered that CTF4 orthologs in plants use common cellular machinery yet accomplish divergent functional outcomes.
Summary Phosphorus is an essential nutrient for plants. It is stored as inorganic phosphate (Pi) in vacuoles of land plants but as inorganic polyphosphate (polyP) in chlorophyte algae. Although it has been known that the SPX-MFS and VPE proteins are respectively responsible for Pi influx and efflux across the tonoplast in land plants, the mechanisms underlying polyP homeostasis and the transition of phosphorus storage forms during the evolution of green plants remain unclear.
