Cluster Roots Research Articles

Combined cellular phenotyping and high-throughput sequencing analysis reveals the symbiotic relationships between different types of macadamia root systems and arbuscular mycorrhizal fungi

Macadamia nuts, scientifically designated as Macadamia integrifolia, are a highly valuable crop that originated in Australia. This study provides a comprehensive examination of the symbiotic relationships between various macadamia root systems and arbuscular mycorrhizal fungi (AMF). The four principal macadamia-producing regions in Yunnan Province were selected for investigation on the basis of meticulous criteria. To determine the AMF infection rate, the roots were stained. Furthermore, high-throughput sequencing was employed to conduct a comprehensive analysis of the fungal diversity in the rhizosphere soil. The findings were definitive, indicating that both normal and cluster roots are capable of establishing a symbiotic relationship with AMF. Secondary forests exhibited significantly elevated fungal diversity relative to normal roots, while cluster roots demonstrated the lowest diversity and notable regional variation, indicating that the environment exerts a considerable influence on inter-root fungi and AMF. The analysis of the fungal community composition revealed that the predominant groups were Ascomycetes and Basidiomycetes. The FUNGuild function prediction clearly indicated distinct differences in the fungal functions of secondary forests, cluster roots, and normal roots. This study provides a scientific foundation for the sustainable development of macadamia nuts and significantly contributes to a deeper comprehension of the intricate interactions between macadamia and AMF, thereby fostering the long-term stable and healthy growth of the macadamia nut industry.

Phosphorus-Use-Efficiency Gene Identification in Fabaceae and RSL2 Expansion in Lupinus albus Is Associated with Low-Phosphorus Adaptation.

Phosphorus is critical for plant growth but often becomes less accessible due to its precipitation with cations in soil. Fabaceae, a diverse plant family, exhibits robust adaptability and includes species like Lupinus albus, known for its efficient phosphorus utilization via cluster roots. Here, we systematically identified phosphorus-utilization-efficiency (PUE) gene families across 35 Fabaceae species, highlighting significant gene amplification in PUE pathways in Fabaceae. Different PUE pathways exhibited variable amplification, evolution, and retention patterns among various Fabaceae crops. Additionally, the number of homologous genes of the root hair development gene RSL2 in L. albus was far more than that in other Fabaceae species. Multiple copies of the RSL2 gene were amplified and retained in L. albus after whole genome triplication. The gene structure and motifs specifically retained in L. albus were different from homologous genes in other plants. Combining transcriptome analysis under low-phosphorus treatment, it was found that most of the homologous genes of RSL2 in L. albus showed high expression in the cluster roots, suggesting that the RSL2 gene family plays an important role in the adaptation process of L. albus to low-phosphorus environments and the formation of cluster roots.

Pinus pinaster root architecture 2 to 5 years after container rearing and outplanting: tropism loss, root clustering and resilience

Pinus pinaster root architecture 2 to 5 years after container rearing and outplanting: tropism loss, root clustering and resilience

Transcriptomics Provide Insights into Early Responses to Sucrose Signaling in Lupinus albus, a Model Plant for Adaptations to Phosphorus and Iron Deficiency.

Phosphorus (P) and iron (Fe) deficiency are major limiting factors for plant productivity worldwide. White lupin (Lupinus albus L.) has become a model plant for understanding plant adaptations to P and Fe deficiency, because of its ability to form cluster roots, bottle-brush-like root structures play an important role in the uptake of P and Fe from soil. However, little is known about the signaling pathways involved in sensing and responding to P and Fe deficiency. Sucrose, sent in increased concentrations from the shoot to the root, has been identified as a long-distance signal of both P and Fe deficiency. To unravel the responses to sucrose as a signal, we performed Oxford Nanopore cDNA sequencing of white lupin roots treated with sucrose for 10, 15, or 20 min compared to untreated controls. We identified a set of 17 genes, including 2 bHLH transcription factors, that were up-regulated at all three time points of sucrose treatment. GO (gene ontology) analysis revealed enrichment of auxin and gibberellin responses as early as 10 min after sucrose addition, as well as the emerging of ethylene responses at 20 min of sucrose treatment, indicating a sequential involvement of these hormones in plant responses to sucrose.

Root growth dynamics, nutrient uptake and use efficiency of Grevillea robusta grown under nitrogen and phosphorus deficiency

Root growth, nutrient uptake, and nutrient use efficiency of a plant is influenced by the nutrient availability in its growing environment. The aim of this study was to investigate the root morphology, nutrient uptake and use efficiency of Grevillea robusta grown in nitrogen (N)- and phosphorus (P)-limited conditions. A hydroponic experiment was conducted for three months in a glasshouse with four nutrient treatments; (i) N-deficient, (ii) P-deficient, (iii) N/P-deficient (co-limitation of N and P), and (iv) control (sufficient amounts of N, P, and other nutrients in the growth medium). The composition and the concentration of each nutrient in the control solution were custom-made based on the growth requirement of G. robusta. N and P concentration in nutrient-deficient media were maintained at 2 ppm. The impact of N- or P-deficiency and their co-limitation on cluster root formation, organ-specific dry matter and nutrient accumulation, N and P uptake and their use efficiencies were measured. P-deficient conditions produced the highest number of cluster roots (24 ± 4) which was comparatively lower than those of N- and N/P-deficient conditions indicating that P-deficiency is the primary factor influencing the formation of cluster roots in G. robusta. The use efficiency of N and P in biomass formation was significantly (p < 0.05) enhanced when their uptake was reduced in response to N- and P-limitation. The efficient internal use of P by G. robusta under N- and N/P-deficiency is indicated by the significant increase in P-remobilization efficiency under these nutrient-deficient conditions.

The white lupin trehalase gene LaTRE1 regulates cluster root formation and function under phosphorus deficiency.

Under phosphorus (P) deficiency, white lupin (Lupinus albus L.) forms specialized root structure, called cluster root (CR), to improve soil exploration and nutrient acquisition. Sugar signaling is thought to play a vital role in the development of CR. Trehalose and its associated metabolites are the essential sugar signal molecules that link growth and development to carbon metabolism in plants, however, their roles in the control of CR are still unclear. Here, we investigated the function of the trehalose metabolism pathway by pharmacological and genetic manipulation of the activity of trehalase in white lupin, the only enzyme that degrades trehalose into glucose. Under P deficiency, validamycin A treatment, which inhibits trehalase, led to the accumulation of trehalose and promoted the formation of CR with enhanced organic acid production, whereas overexpression of the white lupin TREHALASE1 (LaTRE1) led to decreased trehalose levels, lateral rootlet density, and organic acid production. Transcriptomic and virus-induced gene silencing (VIGS) results revealed that LaTRE1 negatively regulates the formation of CRs, at least partially, by the suppression of LaLBD16, whose putative ortholog in Arabidopsis (Arabidopsis thaliana) acts downstream of ARF7- and ARF19-dependent auxin signaling in lateral root formation. Overall, our findings provide an association between the trehalose metabolism gene LaTRE1 and CR formation and function with respect to organic acid production in white lupin under P deficiency.

Attenuated down-regulation of PHOSPHATE TRANSPORTER1 genes as a mechanism for phosphorus sensitivity in phosphorus-efficient Hakea prostrata (Proteaceae)

Abstract Background and aims Phosphorus (P) is an essential plant nutrient and integral for crop yield. However, plants adapted to P-impoverished environments, such as Hakea prostrata (Proteaceae), are often sensitive to P supplies that would be beneficial to other plants. The strategies for phosphate uptake and transport in P-sensitive species have received little attention. Methods Using a recently-assembled transcriptome of H. prostrata, we identified 10 putative members of the PHOSPHATE TRANSPORTER1 (PHT1) gene family, which is responsible for inorganic phosphate (Pi) uptake and transport in plants. We examined plant growth, organ P concentrations and the transcript levels for the eight PHT1 members that were expressed in roots of H. prostrata at Pi supplies ranging from P-impoverished to P-excess. Key results Hakea prostrata plants suppressed cluster root growth above ecologically-relevant Pi supplies, whilst non-cluster root mass ratios were constant. Root P concentrations increased with increasing Pi supply. Of the eight H. prostrata PHT1 genes tested, four had relatively high transcript amounts in young roots suggesting important roles in Pi uptake; however, a maximum five-fold difference in expression between P-impoverished and P-excess conditions indicated a low P-responsiveness for these genes. The HpPHT1;8 and HpPHT1;9 genes were paralogous to Pi-responsive Arabidopsis thaliana PHT1;8 and PHT1;9 orthologues involved in root-to-shoot translocation of P, but only HpPHT1;9 was P responsive. Conclusions An attenuated ability of H. prostrata to regulate PHT1 expression in response to Pi supply is likely responsible for its low capacity to control P uptake and contributes to its high P sensitivity.

Do aluminum (Al)-hyperaccumulator and phosphorus (P)-solubilising species assist neighbouring plants sensitive to Al toxicity and P deficiency?

We aimed to evaluate the facilitation effects of an aluminum (Al) hyperaccumulator species bearing cluster roots, Gevuina avellana, on the seedling growth and performance of an Al-intolerant and phosphorus (P)-deficient-sensitive plant, Vaccinium corymbosum. For this, seedlings of G. avellana and V. corymbosum were grown alone or together as follows: i) two G. avellana seedlings, ii) one G. avellana + one V. corymbosum and iii) two V. corymbosum, in soil supplemented with Al (as Al2(SO4)3) and in the control (without Al supplementation). We determined relative growth rate (RGR), photosynthetic rate, chlorophyll concentration, lipid peroxidation and Al and nutrient concentration [Nitrogen (N), P, potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), and sulfur (S)] in leaves and roots of both species. The results showed that, in general, G. avellana did not assist V. corymbosum to enhance its RGR nor reduce its Al uptake. However, G. avellana assisted V. corymbosum in enhanced N acquisition and, consequently, to increase its chlorophyll concentration and photosynthetic rate. Besides, V. corymbosum had lower lipid peroxidation in leaves when grown in the soil with high Al supplementation in association with G. avellana. Our results suggest a facilitating effect of G. avellana to V. corymbosum when grown in soils with high Al concentration, by enhancing chlorophyll concentrations and photosynthetic rate, and decreasing the oxidative damage to lipids.

Comparative effects of humic acid and charcoal on soil, growth, and biomass properties of lupine (Lupinus albus L.)

Recently, charcoal and humic acid application in soils is a burgeoning area of research due to its profound impact on soil properties and crop yields. Charcoal contributes to improved soil structure, enhanced water-holding capacity, and increased carbon sequestration while humic acid, a component of organic matter, enhances nutrient retention and availability, fostering healthier plant growth and long-term soil health. The experiments were conducted on November 20, 2022, at Grdarasha Research Station, College of Agricultural Engineering Sciences, Salahaddin University-Erbil, Iraq. Two organic sources (humic acid and charcoal) were used to improve soil chemical properties, growth, and biomass characteristics of white lupines. Humic acid at the levels of (0, 10, and 15 g m-2), respectively along with 1 kg m-2 of charcoal. Results showed that essential elements and heavy metals in soil were increased and improved with adding humic acid and charcoal, and then well-affected root ability to uptake nutrients. The great values of germination rate, leaf number (LN), and fresh and dry shoot weights were found when charcoal was stirred to the soil (83.33%, 15.67 LN plant-1, 10.91, and 2.24 t ha-1), respectively. While the longest root length was recorded when humic acid applied at rate of 10 g m-2 (24.22 cm), it was true about the enhancement of cluster roots. Despite that, humic acid at the rate of 15 g m-2 caused to improve fresh and dry root and shoot weights, which were compared to control treatment. The final results indicated that by adding humic acid (H), and charcoal (CH) could improve soil chemical properties, and then may affect positively microorganisms, which can promote plant growth by transforming, solubilizing, and mobilizing soil nutrients. As well, lupinus seemed as phytoremediation (uptake) in case of some heavy metals.

Complexity of a root clustering algorithm for holomorphic functions

Approximating the roots of a holomorphic function in an input box is a fundamental problem in many domains. Most algorithms in the literature for solving this problem are conditional, i.e., they make some simplifying assumptions, such as, all the roots are simple or there are no roots on the boundary of the input box, or the underlying machine model is Real RAM. Root clustering is a generalization of the root approximation problem that allows for errors in the computation and makes no assumption on the multiplicity of the roots. An unconditional algorithm for computing a root clustering of a holomorphic function was given by Yap, Sagraloff and Sharma in 2013 [36]. They proposed a subdivision based algorithm using effective predicates based on Pellet's test while avoiding any comparison with zeros (using soft zero comparisons instead). In this paper, we analyze the running time of their algorithm. We use the continuous amortization framework to derive an upper bound on the size of the subdivision tree. We specialize this bound to the case of polynomials and some simple transcendental functions such as exponential and trigonometric sine. We show that the algorithm takes exponential time even for these simple functions, unlike the case of polynomials. We also derive a bound on the bit-precision used by the algorithm. To the best of our knowledge, this is the first such result for holomorphic functions. We introduce new geometric parameters, such as the relative growth of the function on the input box, for analyzing the algorithm. Thus, our estimates naturally generalize the known results, i.e., for the case of polynomials.

Hierarchical matrix factorization for interpretable collaborative filtering

Matrix factorization (MF) is a simple collaborative filtering technique that achieves superior recommendation accuracy by decomposing the user–item interaction matrix into user and item latent matrices. Because the model typically learns each interaction independently, it may overlook the underlying shared dependencies between users and items, resulting in less stable and interpretable recommendations. Based on these insights, we propose “Hierarchical Matrix Factorization” (HMF), which incorporates clustering concepts to capture the hierarchy, where leaf nodes and other nodes correspond to users/items and clusters, respectively. Central to our approach, called hierarchical embeddings, is the additional decomposition of the latent matrices (embeddings) into probabilistic connection matrices, which link the hierarchy, and a root cluster latent matrix. The embeddings are differentiable, allowing simultaneous learning of interactions and clustering using a single gradient descent method. Furthermore, the obtained cluster-specific interactions naturally summarize user–item interactions and provide interpretability. Experimental results on ratings and ranking predictions show that HMF outperforms existing MF methods, in particular achieving a 1.37 point improvement in RMSE for sparse interactions. Additionally, it was confirmed that the clustering integration of HMF has the potential for faster learning convergence and mitigation of overfitting compared to MF, and also provides interpretability through a cluster-centered case study.

Relictithismia kimotsukiensis, a new genus and species of Thismiaceae from southern Japan with discussions on its phylogenetic relationship.

The family Thismiaceae, known as "fairy lanterns" for their urn- or bell-shaped flowers with basally fused tepals, consists of non-photosynthetic flowering monocots mainly in tropical regions, extending into subtropical and temperate areas. Here, we propose a new mycoheterotrophic genus, Relictithismia Suetsugu & Tagane (Thismiaceae), with its monotypic species Relictithismia kimotsukiensis Suetsugu, Yas.Nakam. & Tagane from Kimotsuki Mountains in the Osumi Peninsula, Kagoshima Prefecture, Kyushu Island, southern Japan. Relictithismia resembles Haplothismia Airy Shaw in having a cluster of tuberous roots, a feature previously observed only in this genus within the family Thismiaceae. However, it differs in having solitary flowers (vs. 2-6-flowered pseudo-raceme in Haplothismia), anther thecae largely separated (vs. connate), and the presence of an annulus (vs. absent). Additionally, Relictithismia differs from the geographically overlapping genus Thismia Griff. in its stamen structure and the position of the annulus. In Relictithismia, the stamens lack connectives, and its free filaments arise from the annulus located inside the perianth mouth, while in Thismia, the stamens typically have connate connectives, forming a staminal tube pendulous from the annulus located at the mouth of the floral tube. Our morphological and phylogenetic data indicated that R. kimotsukiensis holds an early-diverging position within the family, situated outside the Old World Thismia clade. This paper offers an extensive description and color photographs of R. kimotsukiensis, complemented by notes on its phylogenetic relationship and evolutionary history.

Adenanthos species (Proteaceae) in phosphorus-impoverished environments use a variety of phosphorus-acquisition strategies and achieve high-phosphorus-use efficiency.

Soils in south-western Australia are severely phosphorus (P) impoverished, and plants in this region have evolved a variety of P-acquisition strategies. Phosphorus acquisition by Adenanthos cygnorum (Proteaceae) is facilitated by P-mobilizing neighbours which allows it to extend its range of habitats. However, we do not know if other Adenanthos species also exhibit a strategy based on facilitation for P acquisition in P-impoverished environments. We collected leaf and soil samples of Adenanthosbarbiger, A. cuneatus, A.meisneri,A. obovatus, A. sericeus and Adenanthos sp. Whicher Range (G.J. Keighery 9736) growing in their natural habitats at different locations within the severely P-limited megadiverse environment of south-western Australia. Hydroponic experiments were conducted to collect the carboxylates exuded by cluster roots. Pot experiments in soil were carried out to measure rhizosheath phosphatase activity. We found no evidence for facilitation of P uptake in any of the studied Adenanthos species. Like most Proteaceae, A. cuneatus, A. meisneri, A. obovatus, A. sericeus and Adenanthos sp. Whicher Range (G.J. Keighery 9736) expressed P-mining strategies, including the formation of cluster roots. Cluster roots of A. obovatus were less effective than those of the other four Adenanthos species. In contrast to what is known for most Proteaceae, we found no cluster roots for A. barbiger. This species probably expressed a post-fire P-acquisition strategy. All Adenanthos species used P highly efficiently for photosynthesis, like other Proteaceae in similar natural habitats. Adenanthos is the first genus of Proteaceae found to express multiple P-acquisition strategies. The diversity of P-acquisition strategies in these Proteaceae, coupled with similarly diverse strategies in Fabaceae and Myrtaceae, demonstrates that caution is needed in making family- or genus-wide extrapolations about the strategies exhibited in severely P-impoverished megadiverse ecosystems.

The LaCLE35 peptide modifies rootlet density and length in cluster roots of white lupin.

White lupin (lupinus albus L.) forms special bottlebrush-like root structures called cluster roots (CR) when phosphorus is low, to remobilise sparingly soluble phosphates in the soil. The molecular mechanisms that control the CR formation remain unknown. Root development in other plants is regulated by CLE (CLAVATA3/ EMBRYO SURROUNDING REGION (ESR)-RELATED) peptides, which provide more precise control mechanisms than common phytohormones. This makes these peptides interesting candidates to be involved in CR formation, where fine tuning to environmental factors is required. In this study we present an analysis of CLE peptides in white lupin. The peptides LaCLE35 (RGVHy PSGANPLHN) and LaCLE55 (RRVHy PSCHy PDPLHN) reduced root growth and altered CR in hydroponically cultured white lupins. We demonstrate that rootlet density and rootlet length were locally, but not systemically, impaired by exogenously applied CLE35. The peptide was identified in the xylem sap. The inhibitory effect of CLE35 on root growth was attributed to arrested cell elongation in root tips. Taken together, CLE peptides affect both rootlet density and rootlet length, which are two critical factors for CR formation, and may be involved in fine tuning this peculiar root structure that is present in a few crops and many Proteaceae species, under low phosphorus availability.

Morphological and physiological responses of 14 macadamia rootstocks to drought stress and a comprehensive evaluation of drought resistance

Planting macadamia in karst rocky desertification areas has significant ecological and economic benefits. However, the production of macadamia in karst area are facing serious drought challenges due to the poor water holding capacity of soil, and less and uneven precipitation resulting with the rising of temperature in the world. Selecting and breeding drought-resistant rootstocks is one of the main measures to solve this problem in macadamia nut production in karst area. In this study, the morphological and physiological performance of half-sib family offspring of 14 macadamia cultivars were investigated under severe drought conditions and their drought resistance was evaluated comprehensively in order to select the most suitable macadamia rootstocks. Results revealed that the leaves of all rootstocks were damaged after drought stress. Among the tested rootstocks, the leaves of QA5 were damaged the most severely, and the leaves of the whole plants were chlorotic, followed by C11, A4, and NY2, while the symptoms in leaves of O.C and H2 was less obvious after drought stress for 30 d. At the same time, the O.C and H2 had the lowest drought injury index (DII), which was 0.40, while the QA5 had the highest DII value (0.82). The physiological indices, including malonaldehyde (MDA), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), soluble protein (SP), soluble sugar (SS), proline (Pro) and relative electrolyte leakage (REL) increased (Drought tolerance coefficient, DTC > 1) after drought stress, while relative water content of leaves (LRWC), chlorophyll (Chl), relative water content of roots (RRWC) and root activity (RA) decreased (DTC < 1) in all cultivars. Except SP, SS and Pro, there were significant differences in other indexes among different rootstocks. The 13 physiological indices were transformed into seven independent, comprehensive indices through principal component analysis (PCA), whose cumulative contribution ratio reached 82.905%. The 14 rootstocks were divided into 3 categories based on the comprehensive evaluation value (D). The O.C and H2 were clustered into the drought-tolerant group, whose D values were 0.743 and 0.669, respectively. The NY3, 333, 788, NY116, NY1, NY2 were belonged to the intermediate drought tolerance group, the D values were 0.530, 0.508, 0.497, 0.465, 0.457 and 0.441 respectively. Lastly, A16, A4, C11. GR1, 695 and QA5 were clustered into low drought tolerance group with the lowest D values of 0.396, 0.391, 0.360, 0.360, 0.355, 0.324, respectively. The result of stepwise regression analysis showed that MDA, POD, APX, SS, REL, RRWC and RA were the most significant physiological and biochemical indices that played a significant role in drought tolerance, and could be used as the primary evaluation and identification indicators of drought tolerance of macadamia. These results indicated that the drought-resistant rootstocks of macadamia could improve their drought resistance by stimulating the cluster root development, increasing antioxidant enzyme activity and raising the content of osmotic regulatory substances under drought stress. Our study not only provided alternative rootstocks for macadamia drought-resistant cultivation, but also provided the theoretical basis for the drought-resistant rootstock breeding of macadamia by expounding the physiological mechanism of drought-resistance.

Phosphorus absorption kinetics and exudation strategies of roots developed by three lupin species to tackle P deficiency.

Different lupin species exhibited varied biomass, P allocation, and physiological responses to P-deprivation. White and yellow lupins had higher carboxylate exudation rates, while blue lupin showed the highest phosphatase activity. White lupin (Lupinus albus) can produce specialized root structures, called cluster roots, which are adapted to low-phosphorus (P) soil. Blue lupin (L. angustifolius) and yellow lupin (L. luteus), which are two close relatives of white lupin, do not produce cluster roots. This study characterized plant responses to nutrient limitation by analyzing biomass accumulation and P distribution, absorption kinetics and root exudation in white, blue, and yellow lupins. Plants were grown in hydroponic culture with (64µM NaH2PO4) or without P for 31days. Under P limitation, more biomass was allocated to roots to improve P absorption. Furthermore, the relative growth rate of blue lupin showed the strongest inhibition. Under + P conditions, the plant total-P contents of blue lupin and yellow lupin were higher than that of white lupin. To elucidate the responses of lupins via the perspective of absorption kinetics and secretion analysis, blue and yellow lupins were confirmed to have stronger affinity and absorption capacity for orthophosphate after P-deprivation cultivation, whereas white lupin and yellow lupin had greater ability to secrete organic acids. The exudation of blue lupin had higher acid phosphatase activity. This study elucidated that blue lupin was more sensitive to P-scarcity stress and yellow had the greater tolerance of P-deficient condition than either of the other two lupin species. The three lupin species have evolved different adaptation strategies to cope with P deficiency.

Assessing the Nutritional Effect of Lupinus montanus on Zea mays HS-2 (Intercropping) and Identification of Nodular Bacteria through the Use of Rhizotrons

Maize (Zea mays sp.) is one of the most important basic grains in our diets, and it requires high levels of nitrogen and phosphorus for optimum growth. However, phosphorous transitions in forms inaccessible to plants. The Lupinus genus, and more specifically, Lupinus albus, through its root clusters, or proteoid roots, has the ability to solubilize portions of phosphorous when it is found in a limited environment. The objective of the current study was to evaluate the effect of Lupinus montanus under phosphorous stress conditions intercropped with maize, utilizing sandy soils with calcium phosphate bands. Work was conducted in growth chambers using rhizotrons, which allowed the authors to observe the growth and root behavior of both species (Lupinus montanus and maize). The phosphorus analysis in the plant tissue indicated that its concentration in maize was slightly higher in intercropping conditions than in monoculture planting. From this, we concluded that Lupinus montanus is capable of solubilizing portions of phosphorus, making it available for other crops; likewise, we also observed that the proteoid structures did not develop, leaving the study open for other wild species. In conclusion, the use of Lupinus montanus will be as an alternative in favor of more sustainable agricultural methods since it improve soil fertility in phosphorus deficient soils.

Calcifuge and soil-indifferent Proteaceae from south-western Australia: novel strategies in a calcareous habitat

Background and aimsProteaceae are a prominent plant family in south-western Australia. Most Proteaceae are ‘calcifuge’, occurring exclusively on old phosphorus (P)-impoverished acidic soils, with a few ‘soil-indifferent’ species also found on young P-richer calcareous soils. Calcium (Ca)-enhanced P toxicity explains the calcifuge habit of Proteaceae. However, previous research has so far been focused exclusively on the roles of Ca and P in determining Proteaceae distribution, and consequently there is little knowledge on how other soil-based strategies influence this distribution. We aimed to study the effects of young calcareous soils on four soil-grown Proteaceae and assess differences between calcifuge and soil-indifferent Proteaceae to better understand their natural distribution.MethodsTwo calcifuge and two soil-indifferent Proteaceae from south-western Australia were grown in six contrasting soils, including young calcareous, and old acidic soils.ResultsWhen grown in calcareous soils all species showed root growth inhibition, micronutrient deficiency, Ca-enhanced P toxicity, and negative impacts on physiology. Calcifuge species were more sensitive to calcareous soils than soil-indifferent ones, although this varied between genera. Soil-indifferent species tended to produce more cluster roots, release more carboxylates per root mass, and allocate less Ca to their leaves, compared with calcifuges; they also had smaller seeds and were less sensitive to Ca-enhanced P toxicity.ConclusionWe surmise that a combination of these traits allows soil-indifferent species to tolerate calcareous soils. This study provides insight into how Proteaceae respond to young calcareous soils and how this influences their distribution.

Proteaceae species show different strategies for phosphorus acquisition and utilisation in P poor soils in the Mediterranean-type Fynbos ecosystem

Phosphorus is an essential plant macronutrient, but is deficient in soils of nutrient-poor ecosystems. Proteaceae members are characteristic of P-impoverished soils and as such, they have a specialised root adaptation, namely proteoid roots. Proteoid or cluster roots increase P acquisition from the soil for various families that occur in P-impoverished soils. Cluster root function has been shown to be dependent on edaphic features such as soil pH and P availability. Thus, the aim of this study was to assess whether two Protea proteoid rooted systems function with similar adaptive acquisition and utilisation strategies in different P-impoverished soils. Plant and soil material were sampled from two Protea species, P. repens (L.) L. and P. longifolia (A.) A., in their natural habitat. Ecto- and endo-enzymatic activities from samples were conducted to assess their acquisition and utilisation strategies each species employs, as a response to P deficiency. Protea longifolia ecto- and endo-enzymatic activities were significantly higher compared to P. repens. As P. longifolia occurred in more P-deficient soils, the ability to increase P acquisition and utilisation would be beneficial in maintaining its position in the ecosystem. Therefore, P utilisation and acquisition by these two species appear to be influenced by soil P bioavailability; playing an important role in determining adaptive mechanisms utilised by proteoid rooted species.

Overexpression of LaGRAS enhances phosphorus acquisition via increased root growth of phosphorus-deficient white lupin.

The GRAS transcription factors play an indispensable role in plant growth and responses to environmental stresses. The GRAS gene family has extensively been explored in various plant species; however, the comprehensive investigation of GRAS genes in white lupin remains insufficient. In this study, bioinformatics analysis of white lupin genome revealed 51 LaGRAS genes distributed into ten distinct phylogenetic clades. Gene structure analyses revealed that LaGRAS proteins were considerably conserved among the same subfamilies. Notably, twenty-five segmental duplications and a single tandem duplication showed that segmental duplication was the major driving force for the expansion of GRAS genes in white lupin. Moreover, LaGRAS genes exhibited preferential expression in young cluster root and mature cluster roots and may play key roles in nutrient acquisition, particularly phosphorus (P). To validate this, RT-qPCR analysis of white lupin plants grown under +P (normal P) and -P (P deficiency) conditions elucidated significant differences in the transcript level of GRAS genes. Among them, LaGRAS38 and LaGRAS39 were identified as potential candidates with induced expression in MCR under -P. Additionally, white lupin transgenic hairy root overexpressing OE-LaGRAS38 and OE-LaGRAS39 showed increased root growth, and P concentration in root and leaf compared to those with empty vector control, suggesting their role in P acquisition. We believe this comprehensive analysis of GRAS members in white lupin is a first step in exploring their role in the regulation of root growth, tissue development, and ultimately improving P use efficiency in legume crops under natural environments. This article is protected by copyright. All rights reserved.