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The prolonged utilization of copper (Cu)-containing fungicides results in Cu accumulation and affects soil ecological health. Thus, a pot experiment was conducted using Citrus reticulata cv. Shatangju with five Cu levels (38, 108, 178, 318, and 388 mg kg−1) to evaluate the impacts of the soil microbial processes, chemistry properties, and citrus growth. These results revealed that, with the soil Cu levels increased, the soil total Cu (TCu), available Cu (ACu), organic matter (SOM), available potassium (AK), and pH increased while the soil available phosphorus (AP) and alkali-hydrolyzable nitrogen (AN) decreased. Moreover, the soil extracellular enzyme activities related to C and P metabolism decreased while the enzymes related to N metabolism increased, and the expression of soil genes involved in C, N, and P cycling was regulated. Moreover, it was observed that tolerant microorganisms (e.g., p_Proteobacteria, p_Actinobacteria, g_Lysobacter, g_Sphingobium, f_Aspergillaceae, and g_Penicillium) were enriched but sensitive taxa (p_Myxococcota) were suppressed in the citrus rhizosphere. The citrus biomass was mainly positively correlated with soil AN and AP; plant N and P were mainly positively correlated with soil AP, AN, and acid phosphatase (ACP); and plant K was mainly negatively related with soil β−glucosidase (βG) and positively related with the soil fungal Shannon index. The dominant bacterial taxa p_Actinobacteriota presented positively correlated with the plant biomass and plant N, P, and K and was negatively correlated with plant Cu. The dominant fungal taxa p_Ascomycota was positively related to plant Cu but negatively with the plant biomass and plant N, P, and K. Notably, arbuscular mycorrhizal fungi (p_Glomeromycota) were positively related with plant P below soil Cu 108 mg kg−1, and pathogenic fungi (p_Mortierellomycota) was negatively correlated with plant K above soil Cu 178 mg kg−1. These findings provided a new perspective on soil microbes and chemistry properties and the healthy development of the citrus industry at increasing soil Cu levels. [ABSTRACT FROM AUTHOR]

Leaf‐form ferredoxin‐NADP+ oxidoreductases (LFNRs) function in the last step of the photosynthetic electron transport chain, exist as soluble proteins in the chloroplast stroma and are weakly associated with thylakoids or tightly anchored to chloroplast membranes. Arabidopsis thaliana has two LFNRs, and the chloroplast proteins AtTROL and AtTIC62 participate in anchoring AtLFNRs to the thylakoid membrane. By contrast, the membrane anchoring mechanism of rice (Oryza sativa) LFNRs has not been elucidated. Here, we investigated the membrane‐anchoring mechanism of LFNRs and its physiological roles in rice. We characterized the rice protein OsTROL1 based on its homology to AtTROL. We determined that OsTROL1 is also a thylakoid membrane anchor and its loss leads to a compensatory increase in OsTIC62. OsLFNR1 attachment through a membrane anchor depends on OsLFNR2, unlike the Arabidopsis counterparts. In addition, OsTIC62 was more highly expressed in the dark than under light conditions, consistent with the increased membrane binding of OsLFNR in the dark. Moreover, we observed reciprocal stabilization between OsLFNRs and their membrane anchors. In addition, unlike in Arabidopsis, the loss of LFNR membrane anchor affects photosynthesis in rice. Overall, our study sheds light on the mechanisms anchoring LFNRs to membranes in rice and highlights differences with Arabidopsis. Summary statement: Leaf‐form ferredoxin‐NADP+ oxidoreductases (LFNRs) play an important role in regulating ferredoxin (FD)‐dependent electron partitioning in the chloroplast, acting at the branch of photosynthetic electron transfer and reductive metabolism. However, the membrane‐anchoring mechanism of LFNRs and its physiological roles in rice remains largely elusive. Here, we compared the growth phenotype, fresh weight, chlorophyll content, photosynthetic rate, and electron transfer rate among the wild‐type (WT), Oslfnr1‐1, Oslfnr2‐1, Ostic62, Ostrol1‐1 mutants, and Ostrol1‐1 and Ostic62 double mutant. The results showed that mutation of OsLFNRs and their putative anchor partners affects plant growth and photosynthesis. We found that OsTIC62 is necessary for thylakoid‐bound high‐molecular‐weight LFNR complexes, as low‐molecular‐weight LFNR complexes on OsTROL1 and medium‐molecular‐weight complexes are likely a mixture of OsTROL2‒OsLFNR and OsTIC62‒OsLFNR. OsLFNR tightly bind to the thylakoid membrane through OsTIC62 and OsTROL1, this binding stabilizes OsLFNR; also, OsLFNR and its membrane anchors reciprocally stabilize each other. What is more, loss of OsTROL1 leads to a compensatory increase in OsTIC62. In Oslfnr2 mutants, we could not find any OsLFNR complexes in the thylakoid membrane, whereas the Oslfnr1 mutant still had many OsLFNR complexes, which suggested that OsLFNR2 is required for the binding of OsLFNRs to the thylakoid membrane. As the expression pattern of membrane anchors under diurnal conditions has not been reported, we investigated the expression pattern of OsTIC62 under diurnal condition. Gene expression and protein levels suggested that OsTIC62 is highly expressed under dark than in daylight at both the transcript and protein levels, which means that OsTIC62 expression have day‒night rhythm. [ABSTRACT FROM AUTHOR]

SUMMARY: Low soil phosphorus (P) availability is a major limitation for crop production. The molecular mechanisms underlying plant responses and adaptation to phosphate (Pi) deficiency are unclear. OsbHLH6 (hereafter bHLH6), an uncharacterized rice (Oryza sativa) Pi starvation response gene encoding a basic helix‐loop‐helix protein, was identified by yeast two‐hybrid screening using the phosphate response repressor OsSPX4 (hereafter SPX4) as bait. bHLH6 is expressed in shoots and roots, and its expression is significantly induced in shoots by Pi deficiency. bHLH6 overexpression lines showed Pi accumulation and enhanced Pi starvation responses, including upregulation of Pi starvation‐induced genes and longer root hairs. A bhlh6 mutant showed no significant phenotype variation at the seedling stage. A pull‐down assay indicated that bHLH6 had higher binding affinity with SPX4 compared to OsPHR2; therefore, bHLH6 competitively inhibited the interaction of SPX4 and OsPHR2. SPX4 overexpression rescued the Pi accumulation caused by bHLH6 overexpression under high‐ and low‐P conditions. Moreover, overexpression of bHLH6 in an spx4 background did not affect the Pi content of spx4 under high‐ and low‐P conditions. The bhlh6 spx4 double mutant showed lower shoot Pi concentrations and transcript levels of OsPT3 and OsPT10 compared with the spx4 mutant under high‐P conditions. RNA sequencing results indicated that bHLH6 overexpression and spx4 mutant lines share many differentially expressed Pi‐responsive genes. Therefore, bHLH6 is an important regulator for Pi signaling and homeostasis which antagonizes SPX4. This knowledge helps elucidate the molecular regulation of plant adaptation to Pi deficiency and will promote efforts toward the creation of low Pi‐tolerant crops. Significance Statement: This study identified a hitherto uncharacterized phosphate (Pi) starvation‐responsive bHLH family transcription factor, OsbHLH6, in rice (Oryza sativa). OsbHLH6 exclusively interacts with OsSPX4 but not with other SPX proteins and this interaction alters the subcellular localization of OsbHLH6. Our data indicate that OsbHLH6 is a positive regulator of Pi homeostasis and Pi signaling by antagonizing OsSPX4. This knowledge helps elucidate the molecular regulation of plant adaptation to Pi deficiency and will promote efforts toward the genetic improvement of low Pi‐tolerant crops. OsbHLH6 is the first transcription factor in Pi signaling that has been found to regulate SPX proteins. This helps to elucidate the Pi signaling pathway and lays the groundwork for further genetically improving low Pi tolerance in crops. [ABSTRACT FROM AUTHOR]

Auxin plays a pivotal role in many facets of plant development. It acts by inducing the interaction between auxin-responsive [auxin ( AUX)/indole-3-acetic acid ( IAA)] proteins and the ubiquitin protein ligase SCFTIR to promote the degradation of the AUX/ IAA proteins. Other cofactors and chaperones that participate in auxin signaling remain to be identified. Here, we characterized rice ( Oryza sativa) plants with mutations in a cyclophilin gene ( OsCYP2). cyp2 mutants showed defects in auxin responses and exhibited a variety of auxin-related growth defects in the root. In cyp2 mutants, lateral root initiation was blocked after nuclear migration but before the first anticlinal division of the pericycle cell. Yeast two-hybrid and in vitro pull-down results revealed an association between Os CYP2 and the co-chaperone Suppressor of G2 allele of skp1 ( Os SGT1). Luciferase complementation imaging assays further supported this interaction. Similar to previous findings in an Arabidopsis thaliana SGT1 mutant ( atsgt1b), degradation of AUX/ IAA proteins was retarded in cyp2 mutants treated with exogenous 1-naphthylacetic acid. Our results suggest that Os CYP2 participates in auxin signal transduction by interacting with Os SGT1. [ABSTRACT FROM AUTHOR]

Summary Root morphogenesis is crucial for water and nutrient acquisition, but many aspects of root morphogenesis in crops are not well‐understood. Here, we cloned and functionally characterized a key gene for root morphogenesis in rice (Oryza sativa) based on mutant analysis. The stop root morphogenesis 1 (srm1) mutant lacks crown roots (CRs) and lateral roots (LRs) and carries a point mutation in the t‐SNARE coding gene SYNTAXIN OF PLANTS 132 (OsSYP132), leading to a premature stop codon and ablating the post‐transmembrane (PTM) region of OsSYP132. We identified the functional SNARE complex OsSYP132–OsNPSN13–OsSYP71–OsVAMP721/722 and determined that the integrity of the PTM region of OsSYP132 is essential for OsSYP132‐based SNARE complex‐mediated fusion of OsVAMP721/722 vesicles with the plasma membrane. The loss of this region in srm1 disrupts the intercellular trafficking and plasma membrane localization of OsPIN1b, preventing proper auxin distribution in the primordia of CRs and LRs and inhibiting their outgrowth. [ABSTRACT FROM AUTHOR]