First Report of Calonectria montana Causing Leaf Spot on Ligularia fischeri in China.

Ligularia fischeri (Ledeb.) is a perennial herbal plant of Compositae that is cultivated commercially in China as a medicinal, ornamental, and edible plant. Leaf spots were observed in 2-year-old L. fischeri in Benxi County of northeast China, in August 2021. Irregular reddish brown spots ranging from 3 to 11 mm were observed on infected leaves, and each leaf had dozens of spots (Fig. 1). As the disease progressed, the diseased spots withered and the centers fell out, and multiple lesions merge into large diseased spots, causing leaf wilting. The roots and stem bases were not infected during the reproductive stage. More than 37% of the plants in a 18 ha field were infected in 2021. The ten diseased leaves were collected and cut into small (3-5 mm) pieces, which were surface-disinfested by immersing into 1% NaOCl for 2 min and rinsing with sterile distilled water three times. The leaf pieces were then placed on acidified potato dextrose agar (PDA) in petri plates and incubated in the dark at 25°C. Twenty isolates with the same morphological characteristics were obtained. Isolates were further purified by starting a new colony for each isolate from a single spore collected from water agar. Isolate TYTW7 was randomly selected for identification and pathogenicity testing. It grew rapidly and produced profuse aerial mycelia with a carmine red underside. The conidiophores had many fertile branches and formed an elongated stipe with a sphaeropedunculate vesicle at the tip. The one-septate conidia were cylindrical and almost straight with parallel walls and rounded ends. Their sizes ranged from 30.35 to 51.76 × 2.93 to 5.01 µm (n = 100) and the pathogens were initially identified as Calonectria sp. (Crous 2002; Crous et al. 2004; Lombard et al. 2015, 2016). Further confirmation of the identification was determined according to published method (Liu and Chen 2017; Shao and Li 2021). The partial gene regions including the translation elongation factor 1-alpha (GenBank accession no. OP290551), histone H3 (OP290552), calmodulin (OP290553) and ß-tubulin (OP290554) were obtained, and BLAST searches showed 99-100% homology with the ex-type culture CERC 8952 (MF527049, MF527065, MF527081 and MF527107) and phylogenetic analysis combining all loci revealed that the isolate TYTW7 and the type strain of Ca. montana clustered in one group (Fig. 2). Based on morphological characteristics and phylogenetic analysis, isolate TYTW7 was identified as Ca. Montana. Healthy 2-year-old plants were used for the pathogenicity test. A spore suspension (1×105 spores/mL water) was used to inoculate three host plants; sterile water was sprayed on the same number plants serving as a control. The experiment was repeated three times. All plants were incubated at 27±2°C (12h photoperiod) and were evaluated after seven days. The inoculated plants showed lesions on the leaf surface, similar to those in the field, and the control remained symptomless. The pathogens were successfully reisolated and identified by sequencing, and no pathogens were isolated from symptomless control plants. To our knowledge, this is the first report of Ca. montana causing L. fischeri leaf spot. The disease poses a threat to the production and more control strategies are needed on management options to minimize losses.

Anthracnose of Macleaya cordata Caused by Colletotrichum aenigma in China.

Macleaya cordata (Willd.) R. Br. is a perennial herbaceous medicinal plant (Papaveraceae) commercially cultivated in China which has been studied for detumescence, detoxification, and insecticidal effect (Lin et al. 2018). In August 2021, anthracnose was observed in 2-year-old M. cordata plants in Benxi county, northeast China (41°45'48″N, 123°69'15″E). Dozens of irregular reddish-brown spots (3-11 mm) were observed on each diseased leaf. The lesions were covered with a layer of gray-white mycelia. As the disease progressed, the spots became necrosis and perforation or they would merged into large lesions, ultimately resulting in wilted leaves (Fig. 1). More than 33% of the plants in a 16-ha field were infected in 2021. The diseased leaves were collected and cut into 3-8 mm pieces, surface-disinfested by immersing them into 1% NaOCl for 2 min, and rinsed three times with sterile distilled water. They were then dried with sterilized absorbent paper, placed on PDA medium amended with chloramphenicol (40 mg/L), and incubated in darkness at 25°C with a 12-h photoperiod. Twenty isolates (BLH1 to 20) were obtained and purified using a single-spore method. Isolate BLH12 was identified and used for the pathogenicity test. Colonies were sparsely fluffy with smooth edges, and gradually became gray to pale orange from the initial white. The underside of the colonies was pale orange towards the center. Conidia were single-celled, cylindrical, and transparent with broadly blunt ends, measuring (15.13 ± 1.14) × (5.80 ± 0.60) µm (n=50). Appressoria were single-celled, brown-to-dark brown, usually elliptical or irregular, and sometimes lobed. Setae were not observed. The isolate was initially identified as Colletotrichum gloeosporioides complex (Prihastuti et al. 2009). The identification was confirmed as described previously (Weir et al. 2012). The rDNA internal transcribed spacer region (OP415560), the glyceraldehyde-3-phosphate dehydrogenase (OP433642), chitin synthase (OP433643), calmodulin (OP433644), actin (OP433645), glutamine synthetase (OP433646), ß-tubulin (OP433647), and superoxide dismutase (OP433648) gene sequences were obtained (Carbone & Kohn 1999; Weir et al. 2012), and BLAST searches revealed 99-100% homology with the type culture ICMP 18608 (JX010244, JX010044, JX009683, JX009443, JX009744, JX010078, JX010389, and JX010311). A phylogenetic analysis of combining all loci indicated BLH12 and the type strain of C. aenigma were clustered in one group (Fig. 2). Based on the basis of morphological characteristics and phylogenetic relationships, BLH12 was identified as C. aenigma. For the pathogenicity test, healthy 2-year-old plants were sprayed with a BLH12 spore suspension (1 × 105/mL). Control plants were sprayed with sterile water.There were three replicates (five plants each) per treatment. All plants were incubated at 25°C (12-h photoperiod and 86% relative humidity) and examined after 7 days. The experiment was repeated twice. The inoculated plants showed lesions on the leaf surface, similar to those in the field, whereas the control plants were asymptomatic. The pathogen was successfully reisolated and identified as the methods mentioned above. This fungus reportedly infects the leaves of many woody plants in China (Wang et al. 2020; Zhang et al. 2021). This is the first report of C. aenigma causing anthracnose on M. cordata, which will provide an guideline for developing effective field control practices for the disease.

Anthracnose of Brachybotrys paridiformis Caused by Colletotrichum siamense in Northeast China.

Brachybotrys paridiformis Maxim. ex Oliv. (Boraginaceae) is a perennial medicinal plant and vegetable that is cultivated commercially in China. Anthracnose is a devastating disease of B. paridiformis, with annual production losses exceeding 33% based on our survey. In July 2021, anthracnose of B. paridiformis was observed on 2-year-old plants in Shenyang city, Northeast China, which is the most important region for B. paridiformis cultivation. Round or irregular-shaped black spots were exhibited on leaves, with the leaf edges most commonly infected. As the necrosis expanded, the leaves withered and dropped; young leaves were generally not infected (Fig. 1). More than 40% of the plants in a 21-ha sampling field were infected in 2021. Symptomatic leaves (n = 20) were collected and the diseased tissue was cut into small pieces, immersed in 1% NaOCl for 2 min, rinsed three times with sterile water, and placed on acidified potato dextrose agar (PDA) in Petri dishes. After a 3-day incubation in darkness at 25 °C, 18 suspected single-pure morphologically identical Colletotrichum isolates were obtained and sequenced. Isolate SQZ9 was randomly selected and identified. Colonies on PDA were initially white, but gradually became pale brownish with a reverse side that was pale yellowish to pinkish. Aerial mycelia were grayish-white, dense, and cottony, with microsclerotia detected on some aging mycelia. The detected single-celled conidia (11.65-17.25 × 4.25-6.15 µm; n = 50) were fusiform to cylindrical with obtuse to slightly rounded ends. Appressoria were ovoid to clavate and medium brown. Setae were not observed. The morphological characteristics were similar to those of Colletotrichum spp. (Prihastuti et al. 2009; Weir et al. 2012). Initial BLAST searches of the GenBank database revealed the SQZ9 rDNA internal transcribed spacer region (OP389109, 566 bp), glyceraldehyde-3-phosphate dehydrogenase (OP407730, 260 bp), chitin synthase (OP407731, 301 bp), calmodulin (OP407732, 712 bp), actin (OP407733, 282 bp), glutamine synthetase (OP407734, 909 bp), ß-tublin (OP407735, 498 bp), and superoxide dismutase (OP407736, 396 bp) sequences were respectively 99%-100% similar to the C. siamense type strain JX010278, JX010019, JX009709, GQ856775, GQ856730, JX010100, JX010410, and JX010332 sequences (Carbone & Kohn 1999; Moriwaki & Tsukiboshi 2009; Stephenson et al. 1997). The SQZ9 identity was confirmed by constructing a phylogenetic tree combining all loci, which grouped the isolate and the C. siamense type strain in the same clade (Fig. 2). For pathogenicity tests, 15 healthy 2-year-old plants (3 plants per pot) were spray-inoculated with SQZ9 conidial suspension (1 × 105 conidia/mL) at 2 mL per plant. Same number of plants sprayed with water were used as control. This experiment was repeated twice. All plants were covered with clear plastic bags for 72 h to maintain high humidity and then placed in a greenhouse (29 °C, natural light, and 85% relative humidity). After six days, the inoculated leaves exhibited symptoms that were similar to those observed in the field, but the controls were symptomless. The same fungus was recovered from inoculated symptomatic leaves, and its identity was confirmed by sequencing and a phylogenetic analysis. This is the first report of C. siamense causing anthracnose on B. paridiformis in China. Future studies should assess the effectiveness of chemical and biological control measures for managing this disease.

Anthracnose of Tribulus terrestris Caused by Colletotrichum truncatum in Northeast China.

Tribulus terrestris L. is an annual herbaceous medicinal plant of Zygophyllaceae, which is cultivated commercially in China. Subrotund or irregular gray, sunken, necrotic spots ranging from 2 to 9 mm were observed on diseased leaves of T. terrestris landrace in Fushun County, Liaoning Province of northeast China in July 2021, with more than 32% of the plants being infected in a 18-ha field. The symptoms first appeared on older leaves and gradually spread to younger leaves. The lesions developed a white center gradually and became perforated; multiple lesions could coalesce (Fig. 1). Ten symptomatic leaves were collected and the diseased tissues were cut into small pieces, immersed in 1% NaOCl for 2 min, rinsed three times with sterile water, and placed on acidified potato dextrose agar (PDA) in Petri dishes at 25°C in darkness. Fifteen suspected Colletotrichum single-spore fungal isolates (JL1 to JL15) with consistent morphological characteristics were obtained, and isolate JL6 was selected for identification and pathogenicity testing. Colonies on PDA were flat with an entire margin, dense and white at first, then became dark gray with numerous black microsclerotia and formed a concentric circular pattern with aging. Conidia were single-celled, sickle-curved with a tapered tip and truncate base, ranging from 16.46 to 20.26 µm in length and 2.81 to 3.96 µm in width (n=100). Setae were dark brown, septate, straight with a slightly acute tip, 75.45 to 135.63×3.19 to 4.95 µm in size. Appressoria were dark brown, round or irregular, mostly in groups. All characteristics were consistent with the descriptions of C. truncatum (Damm et al. 2009). Further confirmation of the identification was determined according to methods described previously (Damm et al. 2009). The rDNA internal transcribed spacer region (OP364400, 585 bp), and actin (OP380867, 290 bp), beta-tubulin (OP380868, 498 bp), chitin synthase 1 (OP380869, 277 bp), glyceraldehyde-3-phosphate dehydrogenase (OP380870, 280 bp), and histone (OP380871, 411 bp) genes were amplified by PCR and sequenced (Carbone and Kohn 1999; Glass and& Donaldson 1995; Guerber et al. 2003; O'Donnell and Cigelnik 1997). BLAST results showed 98-100% similarity at 85-97% coverage compared to the corresponding sequences of the type strain CBS 151.35 (GU227862, GU227960, GU228156, GU228352, GU228254, and GU228058). Phylogenetic analysis combining all loci revealed that the isolate JL6 and the type strains of C. truncatum clustered in one group (Fig. 2). One-year-old healthy seedlings of T. terrestris (cultivar: landrace) were used for pathogenicity test. Suspension (1×105 conidia/mL) of isolate JL6 was sprayed on ten seedlings, and ten seedlings sprayed with sterilized distilled water were used as the control. Three replicates were performed on each treatment. All plants were kept at 28±1°C (12 h photoperiod), and were evaluated after 7 days. The inoculated plants showed lesions on the leaf surface, similar to those in the field, and the control remained symptomless. The pathogen was successfully reisolated and identified using the methods mentioned above. To our knowledge, this is the first report of C. truncatum causing anthracnose on T. terrestris, which will provide valuable information for designing strategies to manage anthracnose on T. terrestris.

Cardiac Fibroblast-Specific Knockout of PGC-1α Accelerates AngII-Induced Cardiac Remodeling.

Cardiac remodeling consisted of ventricular hypertrophy and interstitial fibrosis is the pathological process of many heart diseases. Fibroblasts as one of the major cells in the myocardium regulate the balance of the generation and degeneration of collagen, and these cells transform toward myofibroblasts in pathological state, contributing to the remodeling of the heart. Peroxisome proliferator-activated receptor-γ (PPAR-γ) coactivator-1α (PGC-1α) is vital to the function of mitochondria, which contributes to the energy production and reactive oxidative species (ROS)-scavenging activity in the heart. In this study, we found that fibroblast-specific PGC-1α KO induced cardiac remodeling especially fibrosis, and Angiotensin II (AngII) aggravated cardiac fibrosis, accompanied with a high level of oxidative stress response and inflammation.

Senescent T Cell Induces Brown Adipose Tissue "Whitening" Via Secreting IFN-γ.

Aging-associated chronic inflammation is a key contributing factor to a cluster of chronic metabolic disorders, such as cardiovascular disease, obesity, and type 2 diabetes. Immune cells particularly T cells accumulate in adipose tissue with advancing age, and there exists a cross talk between T cell and preadipocyte, contributing to age-related adipose tissue remodeling. Here, we compared the difference in morphology and function of adipose tissue between young (3-month-old) and old (18-month-old) mice and showed the phenomenon of brown adipose tissue (BAT) "whitening" in old mice. Flow cytometry analysis suggested an increased proportion of T cells in BAT of old mice comparing with the young and exhibited senescent characteristics. We take advantage of coculture system to demonstrate directly that senescent T cells inhibited brown adipocyte differentiation of preadipocytes in adipose tissue. Mechanistically, both in vitro and in vivo studies suggested that senescent T cells produced and released a higher level of IFN-γ, which plays a critical role in inhibition of preadipocyte-to-brown adipocyte differentiation. Taken together, the data indicate that senescent T cell-derived IFN-γ is a key regulator in brown adipocyte differentiation.

T-cell senescence accelerates angiotensin II-induced target organ damage.

AIMS: Aging is a risk factor for cardiovascular diseases and adaptive immunity has been implicated in angiotensin (Ang) II-induced target organ dysfunction. Herein, we sought to determine the role of T-cell senescence in Ang II-induced target organ impairment and to explore the underlying mechanisms. METHODS AND RESULTS: Flow cytometric analysis revealed that T cell derived from aged mice exhibited immunosenescence. Adoptive transfer of aged T cells to immunodeficient RAG1 KO mice accelerates Ang II-induced cardiovascular and renal fibrosis compared with young T-cell transfer. Aged T cells also promote inflammatory factor expression and superoxide production in these target organs. In vivo and in vitro studies revealed that Ang II promotes interferon-gamma (IFN-γ) production in the aged T cells comparing to young T cells. Importantly, transfer of senescent T cell that IFN-γ KO mitigates the impairment. Aged T-cell-conditioned medium stimulates inflammatory factor expression and oxidative stress in Ang II-treated renal epithelial cells compared with young T cells, and these effects of aged T-cell-conditioned medium are blunted after IFN-γ-neutralizing antibody pre-treatment. CONCLUSION: These results provide a significant insight into the contribution of senescent T cells to Ang II-induced cardiovascular dysfunction and provide an attractive possibility that targeting T cell specifically might be a potential strategy to treat elderly hypertensive patients with end-organ dysfunction.

Perivascular adipose tissue-derived stromal cells contribute to vascular remodeling during aging.

Aging is an independent risk factor for vascular diseases. Perivascular adipose tissue (PVAT), an active component of the vasculature, contributes to vascular dysfunction during aging. Identification of underlying cell types and their changes during aging may provide meaningful insights regarding the clinical relevance of aging-related vascular diseases. Here, we take advantage of single-cell RNA sequence to characterize the resident stromal cells in the PVAT (PVASCs) and identified different clusters between young and aged PVASCs. Bioinformatics analysis revealed decreased endothelial and brown adipogenic differentiation capacities of PVASCs during aging, which contributed to neointimal hyperplasia after perivascular delivery to ligated carotid arteries. Mechanistically, in vitro and in vivo studies both suggested that aging-induced loss of peroxisome proliferator-activated receptor-γ coactivator-1 α (PGC1α) was a key regulator of decreased brown adipogenic differentiation in senescent PVASCs. We further demonstrated the existence of human PVASCs (hPVASCs) and overexpression of PGC1α improved hPVASC delivery-induced vascular remodeling. Our finding emphasizes that differentiation capacities of PVASCs alter during aging and loss of PGC1α in aged PVASCs contributes to vascular remodeling via decreased brown adipogenic differentiation.

Loss of miR-146b-3p Inhibits Perivascular Adipocyte Browning with Cold Exposure During Aging.

PURPOSE: Pathological changes of the perivascular adipose tissue (PVAT) are directly associated with increased risk of age-related vascular diseases. MicroRNAs regulate adipocyte biological functions including adipogenic differentiation and white adipocyte browning. The present study aims to determine whether miR-146b-3p is involved in the regulation of perivascular adipocyte browning during aging. METHODS: We utilized a cold-induced animal model to investigate the effect of aging on perivascular adipocyte browning. We also detected the miR-146b-3p expression in the PVAT of young or old mice after cold stimulus. We further investigated the role of miR-146b-3p in regulating perivascular adipocyte browning in vitro and in vivo via administrating miRNA mimics or inhibitors. RESULTS: Old mice showed decrease of perivascular adipocyte browning and downregulation of miR-146b-3p expression in the PVAT after cold stimulus. Oil red O staining and qPCR indicated that aging perturbed preadipocyte to brown adipocyte differentiation, and expression of miR-146b-3p gradually increased during differentiation. MiR-146b-3p inhibitors blocked brown adipocyte differentiation in young preadipocytes, whereas miR-146b-3p mimics rescued the differentiation of the old preadipocytes. Finally, miR-146b-3p knocks down inhibited perivascular adipocyte browning in young mice after cold stimulus. CONCLUSION: Aging inhibits perivascular adipocyte browning, and loss of miR-146b-3p is a potential regulator for this process.

A2A Receptor Activation Attenuates Hypertensive Cardiac Remodeling via Promoting Brown Adipose Tissue-Derived FGF21.

Adipocytes play important roles in regulating cardiovascular health and disease. However, the molecular mechanism underlying the endocrine role of brown adipose tissue (BAT) in pathological cardiac remodeling remains unknown. Herein we show that adenosine A2A receptor (A2AR) knockout (A2ARKO) causes interscapular BAT (iBAT) dysfunction, leading to accelerated cardiac remodeling in hypertension compared with wild-type (WT) mice. Surgical iBAT depletion induces dramatic cardiac remodeling in WT but not in A2ARKO hypertensive mice. AMPK/PGC1α signaling-induced fibroblast growth factor 21 (FGF21) in brown adipocytes is required for A2AR-mediated inhibition of hypertensive cardiac remodeling. Recombinant FGF21 administration improves cardiac remodeling in iBAT-depleted hypertensive mice. More importantly, brown adipocyte-specific A2ARKO inhibits FGF21 production and accelerates cardiac damage in hypertension. Consistently, brown adipocyte-specific FGF21 knockout abolishes the effects of A2AR agonism in attenuating hypertensive cardiac remodeling. Our findings reveal a distinctive endocrine role of BAT in hypertensive cardiac remodeling via activating A2AR/FGF21 pathway.

Zea mays Fe deficiency-related 4 (ZmFDR4) functions as an iron transporter in the plastids of monocots.

Iron (Fe)-homeostasis in the plastids is closely associated with Fe transport proteins that prevent Fe from occurring in its toxic free ionic forms. However, the number of known protein families related to Fe transport in the plastids (about five) and the function of iron in non-green plastids is limited. In the present study, we report the functional characterization of Zea mays Fe deficiency-related 4 (ZmFDR4), which was isolated from a differentially expressed clone of a cDNA library of Fe deficiency-induced maize roots. ZmFDR4 is homologous to the bacterial FliP superfamily, coexisted in both algae and terrestrial plants, and capable of restoring the normal growth of the yeast mutant fet3fet4, which possesses defective Fe uptake systems. ZmFDR4 mRNA is ubiquitous in maize and is inducible by iron deficiency in wheat. Transient expression of the 35S:ZmFDR4-eGFP fusion protein in rice protoplasts indicated that ZmFDR4 maybe localizes to the plastids envelope and thylakoid. In 35S:c-Myc-ZmFDR4 transgenic tobacco, immunohistochemistry and immunoblotting confirmed that ZmFDR4 is targeted to both the chloroplast envelope and thylakoid. Meanwhile, ultrastructure analysis indicates that ZmFDR4 promotes the density of plastids and accumulation of starch grains. Moreover, Bathophenanthroline disulfonate (BPDS) colorimetry and inductively coupled plasma mass spectrometry (ICP-MS) indicate that ZmFDR4 is related to Fe uptake by plastids and increases seed Fe content. Finally, 35S:c-Myc-ZmFDR4 transgenic tobacco show enhanced photosynthetic efficiency. Therefore, the results of the present study demonstrate that ZmFDR4 functions as an iron transporter in monocot plastids and provide insight into the process of Fe uptake by plastids.

CSN6, a subunit of the COP9 signalosome, is involved in early response to iron deficiency in Oryza sativa.

The COP9 signalosome (CSN) plays an important role in proteasome-mediated degradation by regulating CUL1 rubylation of the SCF ligase and is involved in many crucial biological processes. Here, we demonstrate a link between IDEF1 accumulation and the decline in COP9 derubylation activity in response to iron deficiency (-Fe) in rice (Oryza sativa). CSN6 expression is rapidly down-regulated during Fe depletion, contributing to reduced CSN activity, as judged by CSN5 and CUL1 expression, indicating CSN6 is involved in the early stage response of -Fe. In contrast to CSN6, the IDEF1 protein and expression of several iron uptake/utilisation-related genes are increased in response to -Fe. Thus, we constructed CSN6 transgenic sense and antisense lines and found that experimental depletion of CSN6 results in accumulation of the IDEF1 protein and up-regulation of several iron uptake/utilisation-related genes. Furthermore, IDEF1 can be decorated with K48-linked polyubiquitin and degraded via the 26S proteasome. Accumulated IDEF1 in antisense lines led to increased chlorophyll and Fe content in seedlings during -Fe. Collectively, the cellular CSN6 level is decreased during early stages of -Fe to ensure the rapid accumulation of IDEF1, which in turn up-regulates several iron uptake/utilisation-related genes to help overcome -Fe stress in rice.

OsSEC24, a functional SEC24-like protein in rice, improves tolerance to iron deficiency and high pH by enhancing H(+) secretion mediated by PM-H(+)-ATPase.

Iron is abundant in the soil, but its low solubility in neutral or alkaline soils limits its uptake. Plants can rely on rhizosphere acidification to increase iron solubility. OsSEC27p was previously found to be a highly up-regulated gene in iron-deficient rice roots. Here, pH-dependent complementation assays using yeast mutants sec24Δ/SEC24 and sec27Δ/SEC27 showed that OsSEC27 could functionally complement SEC24 but not SEC27 in yeast; thus, it was renamed as OsSEC24. We found that OsSEC24-transgenic tobacco plants increased the length and number of roots under iron deficiency at pH 8.0. To explore how OsSEC24 confers tolerance to iron deficiency, we utilized transgenic tobacco, rice and rice protoplasts. H(+) flux measurements using Non-invasive Micro-test Technology (NMT) indicated that the transgenic OsSEC24 tobacco and rice enhanced H(+) efflux under iron deficiency. Conversely, the application of plasma membrane PM-H(+)-ATPase inhibitor vanadate elucidated that H(+) secretion increased by OsSEC24 was mediated by PM-H(+)-ATPase. OsPMA2 was used as a representative of iron deficiency-responsive PM-H(+)-ATPases in rice root via RT-PCR analysis. In transgenic rice protoplasts OsPMA2 was packaged into OsSEC24 vesicles after export from the ER through confocal-microscopy observation. Together, OsSEC24 vesicles, along with PM-H(+)-ATPases stimulate roots formation under iron deficiency by enhancing rhizosphere acidification.