Root Responses Research Articles

Functional Characterization on Wheat Protein Kinase Gene <i>TaSnRK2.1</i> in Mediating Plant Resistance to Drought Stress

The protein kinase type of sucrose non-fermenting-1 related protein kinase 2 (SnRK2) plays an important role in regulating plant growth and development and in mediating plant resistance to abiotic stresses given that it involves transduction of distinct internal and abiotic stress signaling. In this study, <i>TaSnRK2.1</i>, a gene of SnRK2 family in wheat, was investigated focusing on its molecular characterization, expression pattern upon drought stress, and the biological function in mediating plant drought tolerance. At nucleic acid level, <i>TaSnRK2.1</i> is highly homologous to its counterparts of SnRK2 kinase family genes in species of Polish wheat and barley, whose translated protein harbors a conserved catalytic domain of Ser/Thr kinase domain (aa 62-aa 318). Under a 48 h-regime drought treatment, the transcripts of <i>TaSnRK2.1</i> showed obvious response in roots and leaves, with the highest expression level reached at 24 h after treatment and maintaining a high level to 48 h under drought condition. Meanwhile, the transcripts of <i>TaSnRK2.1</i> in both roots and leaves induced by drought were recovered following the normal recovery treatment. Gene transgene analysis indicated that compared with wild type control (WT), the tobacco line with sense-overexpression of <i>TaSnRK2.1</i> (Sen 1) enlarged plant growth phenotypes, increased dry weights, promoted stomata closing, increased contents of cellular osmtic-regulatory substances including proline, soluble protein, and soluble sugar, enhanced photosynthetic capacity and elevated cellular protective enzyme activities under drought treatment. In contrast, the line with antisense-expression of <i>TaSnRK2.1</i> (Anti 1) reduced plant growth phenotypes, decreased biomass, slowed stomata closing, decreased the contents of cellular osmtic-regulatory substances, photosynthetic capacity and protective enzyme activities compared with WT plants treated by drought stress. Our investigation suggested that <i>TaSnRK2.1</i> is sensitive in response to drought signaling at transcriptional level that confers enhanced plant drought resistance by regulating physiological processes associated with stomata movement, cellular osmotic-regulatory substance metabolism, photosynthetsis, and protective enzyme activities.

Arabidopsis thaliana B-GATA factors repress starch synthesis and gravitropic growth responses.

Plants perceive the direction of gravity during skotomorphogenic growth, and of gravity and light during photomorphogenic growth. Gravity perception occurs through the sedimentation of starch granules in shoot endodermal and root columella cells. In this study, we demonstrate that the Arabidopsis thaliana GATA factors GNC (GATA, NITRATE-INDUCIBLE, CARBON METABOLISM-INVOLVED) and GNL/CGA1 (GNC-LIKE/CYTOKININ-RESPONSIVE GATA1) repress starch granule growth and amyloplast differentiation in endodermal cells. In our comprehensive study, we analysed gravitropic responses in the shoot, root and hypocotyl. We performed an RNA-seq analysis, used advanced microscopy techniques to examine starch granule size, number and morphology and quantified transitory starch degradation patterns. Using transmission electron microscopy, we examined amyloplast development. Our results indicate that the altered gravitropic responses in hypocotyls, shoots and roots of gnc gnl mutants and GNL overexpressors are due to the differential accumulation of starch granules observed in the GATA genotypes. At the whole-plant level, GNC and GNL play a more complex role in starch synthesis, degradation and starch granule initiation. Our findings suggest that the light-regulated GNC and GNL help balance phototropic and gravitropic growth responses after the transition from skotomorphogenesis to photomorphogenesis by repressing the growth of starch granules.

MIZU-KUSSEI1 (MIZ1) and GNOM/MIZ2 control not only positive hydrotropism but also phototropism in Arabidopsis roots.

In response to unilateral blue light illumination, roots of some plant species such as Arabidopsis thaliana exhibit negative phototropism (bending away from light), which is important for light avoidance in nature. MIZU-KUSSEI1 (MIZ1) and GNOM/MIZ2 are essential for positive hydrotropism (i.e. in the presence of a moisture gradient, root bending towards greater water availability). Intriguingly, mutations in these genes also cause a substantial reduction in phototropism. Here, we examined whether the same tissue-specific sites of expression required for MIZ1- and GNOM/MIZ2-regulated hydrotropism in Arabidopsis roots are also required for phototropism. The attenuated phototropic response of miz1 roots was completely restored when a functional MIZ1-green fluorescent protein (GFP) fusion was expressed in the cortex of the root elongation zone but not in other tissues such as root cap, meristem, epidermis, or endodermis. The hydrotropic defect and reduced phototropism of miz2 roots were restored by GNOM/MIZ2 expression in either the epidermis, cortex, or stele, but not in the root cap or endodermis. Thus, the sites in root tissues that are involved in the regulation of MIZ1- and GNOM/MIZ2-dependent hydrotropism also regulate phototropism. These results suggest that MIZ1- and GNOM/MIZ2-mediated pathways are, at least in part, shared by hydrotropic and phototropic responses in Arabidopsis roots.

Exogenous Melatonin Enhances the Low Phosphorus Tolerance of Barley Roots of Different Genotypes.

Melatonin (N-acetyl-5-methoxytryptamine) plays an important role in plant growth and development, and in the response to various abiotic stresses. However, its role in the responses of barley to low phosphorus (LP) stress remains largely unknown. In the present study, we investigated the root phenotypes and metabolic patterns of LP-tolerant (GN121) and LP-sensitive (GN42) barley genotypes under normal P, LP, and LP with exogenous melatonin (30 μM) conditions. We found that melatonin improved barley tolerance to LP mainly by increasing root length. Untargeted metabolomic analysis showed that metabolites such as carboxylic acids and derivatives, fatty acyls, organooxygen compounds, benzene and substituted derivatives were involved in the LP stress response of barley roots, while melatonin mainly regulated indoles and derivatives, organooxygen compounds, and glycerophospholipids to alleviate LP stress. Interestingly, exogenous melatonin showed different metabolic patterns in different genotypes of barley in response to LP stress. In GN42, exogenous melatonin mainly promotes hormone-mediated root growth and increases antioxidant capacity to cope with LP damage, while in GN121, it mainly promotes the P remobilization to supplement phosphate in roots. Our study revealed the protective mechanisms of exogenous MT in alleviating LP stress of different genotypes of barley, which can be used in the production of phosphorus-deficient crops.

Genetic Analysis of Maize Response to Salt Stress in Hydroponic Medium

The productivity of maize (Zea mays L.) from the farmers’ fields has been characterized as being low due to salinity among other contributing factors. In this study the use of phenotypic traits as a selection criterion and screening of maize genotypes for tolerance to salt stress was investigated. The objectives of this study were therefore to i) estimate heritability for genotypic response to root and shoot length ii) ascertain an appropriate genotypic maize screening criterion in saline medium and iii) identify tolerant maize genotypes in hydroponic medium. The experiment was set up as 5 x 11 factorial completely randomized design (CRD) with three replications at the University of Zambia, pathology laboratory. Thus 11 genotypes were evaluated in five doses of salinity concentrations giving 55 experimental units. Genotypes exhibited significant differences (P&lt; 0.05) in response to both parameters (root and shoot length) across salinity concentrations. Similarly the response of root and shoot length in different salinity concentration across genotypes was also significant (P&lt; 0.001). The entry based heritability estimate was found to be 0.76 and 0.18 for responses to root and shoot respectively. Shoot length was identified as a key trait to utilize in screening maize genotypes for tolerance to salt stress under hydroponic conditions despite possessing a low heritability estimate. In this study tolerant genotypes to salt stress were identified as ZHYB 2, ZHYB 7 and ZHYB 11.

Shoot and Root Responses of Mung Beans (Vigna radiata L.) to Changing Solution Phosphorus Conditions

ABSTRACT Context: Previous research using soil has shown that mung bean (Vigna radiata L.) exhibits minimal root length response to elevated soil solution P concentrations, so does P uptake rate compensate? Aim: We hypothesized that when a mung bean plant growing in a nutrient solution low in P accesses a short-term adequate P supply it would increase P uptake through root plasticity. Methods: Mung bean seedlings were grown for 33 d in nutrient solutions with P concentrations of ranging from 1.6 to 6.6 mg L−1 and then transferred to an 8.2 mg L−1 P, 32P labeled solution and plants harvested 4 and 9 d after transfer. Key results: Plant growth and P uptake were increased by increasing short-term P supply. P uptake from the transfer solution doubled in the low P plants between 4 and 9 d, while in the high P plants there was a 2.5-fold increase. After 9 d in the transfer solution, 26.0% of the P in the low P plants was derived from the transfer solution compared to 18.3% in the high P plants. Between 4 and 9 d, total root length doubled in the low P plants and there was no significant increase in the high P plants. Conclusion: The results indicated that an increase in fine root length was the primary mechanism responsible for the increased P uptake upon transfer to a high P solution. Implications: In low P soils banding of P will result in increased root and shoot growth in mung beans.

CG hypermethylation of the bHLH39 promoter regulates its expression and Fe deficiency responses in tomato roots.

Iron (Fe) is an essential micronutrient for all organisms, including plants, whose limited bioavailability restricts plant growth, yield, and nutritional quality. While the transcriptional regulation of plant responses to Fe deficiency have been extensively studied, the contribution of epigenetic modulations, such as DNA methylation, remains poorly understood. Here, we report that treatment with a DNA methylase inhibitor repressed Fe deficiency-induced responses in tomato (Solanum lycopersicum) roots, suggesting the importance of DNA methylation in regulating Fe deficiency responses. Dynamic changes in the DNA methylome in tomato roots responding to short-term (12hours) and long-term (72hours) Fe deficiency identified many differentially methylated regions (DMRs) and DMR-associated genes. Most DMRs occurred at CHH sites under short-term Fe deficiency, whereas they were predominant at CG sites following long-term Fe deficiency. Furthermore, no correlation was detected between the changes in DNA methylation levels and the changes in transcript levels of the affected genes under either short-term or long-term treatments. Notably, one exception was CG hypermethylation at the bHLH39 promoter, which was positively correlated with its transcriptional induction. In agreement, we detected lower CG methylation at the bHLH39 promoter and lower bHLH39 expression in MET1-RNA interference lines compared with wild-type seedlings. Virus-induced gene silencing of bHLH39 and luciferase reporter assays revealed that bHLH39 is positively involved in the modulation of Fe homeostasis. Altogether, we propose that dynamic epigenetic DNA methylation in the CG context at the bHLH39 promoter is involved in its transcriptional regulation, thus contributing to the Fe deficiency response of tomato.

Strigolactone Mediates Moso Bamboo Root Response to Phosphate Stress.

Both phosphate (Pi) deficiency and high Pi significantly affect moso bamboo growth and degrade bamboo forests. A novel plant hormone, strigolactone (SL), plays a crucial role in root growth under low Pi, but the SL regulatory mechanism has not been systematically reported in moso bamboo. In our study, we investigated the SL-mediated root growth mechanism in response to Pi stress in moso bamboo. With the decrease of the Pi level, 5-deoxystrigol and strigol significantly increased in the root exudates. Transcriptome sequencing of the primary root tip and lateral root primordium zone (LRP) under low, sufficient, and high Pi indicated that SL-biosynthesis and -signaling changes are part of the early root responses. The effects of the SL analogue (rac-GR24) and SL inhibitor (TIS108) on the root architecture under low and high Pi revealed that SL mediates bamboo root responses by regulating its biosynthesis and signal transduction and influencing other hormone pathways.

Gender-specific responses of Salix viminalis roots in morphology and physiology subjected to flooding

Flooding is one of the most common abiotic stresses that plants suffer. Roots are organs that directly sense anoxic environments, but there are few researches on the response of roots to flooding. In this research, the responses of male and female Salix viminalis plants to flooding were investigated by examining the morphological and physiological responses of roots. Our results showed that primary roots (PRs) growth was significantly inhibited and damaged to a certain extent. However, adventitious roots (ARs) formed in a short time and were essential for plants to endure flooding. To cope with flooding stress, the antioxidant enzyme activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) increased. Although Pro-contents increased, they were too low to contribute significantly to osmotic adjustment. The anaerobic respiration metabolic pathway was also activated, as proven by increased pyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH), and lactate dehydrogenase (LDH) activities, and the ethanol metabolism pathway might have a key function in adapting to the hypoxic environment for S. viminalis. In addition, increased non-structural carbohydrates (NSCs) of starch and soluble sugar (SS) contents indicated that quiescence strategy might exist in S. viminalis. Overall, there were no significant differences between males and females under flooding stress, and both genders exhibited strong adaptability to the flooding environment. Therefore, two genders of S. viminalis could be applied in the riparian zone.

Plant functional types and microtopography mediate climate change responses of fine roots in forested boreal peatlands

Peatlands store one-third of the world’s soil carbon, and their climate change response is a key unknown in the global carbon cycle-climate change feedback. In particular, peatland fine root responses to varied environmental changes are poorly constrained. Here, we synthesized fine root responses to warming and water level drawdown by performing a meta-analysis of existing data from boreal forested peatlands. We found seven studies and evaluated root responses from 65 observations. Overall, both warming (from 0 to 9.0°C) and water level drawdown (from 4.0 to 62.5 cm) increased fine root growth by over an order of magnitude, with plant functional type (PFT; graminoid, shrub, and tree) better predicting fine root biomass than treatment magnitude. We observed stronger responses for trees (+374.5% for warming and +868.6% for water level drawdown) than for shrubs (+44.0% for warming and +11.5% for water level drawdown) and graminoids (+59.5% for warming and −59.8% for water level drawdown). Among PFTs, tree fine roots increased significantly and non-linearly with increasing warming treatment, while graminoid fine roots responded significantly to lowering water level, decreasing 1.7% for every 1 cm decrease in water level. Fine roots in hollows, especially of shrubs, increased more strongly than those in hummocks, suggesting a possible flattening of peatland topography with sustained hollow growth from extended warming. Our synthesis highlights the important role of PFT’s in modulating fine root responses and the need for additional belowground data from these carbon-rich and globally relevant peatland soils. The altered fine root growth documented here, implies possible shifts in plant nutrient and water uptake as well as root inputs to soil carbon stocks, which in turn could strongly moderate and shape boreal peatland responses to future climate change.

Short-term exposition to acute cadmium toxicity induces the loss of root gravitropic stimuli perception through PIN2-mediated auxin redistribution in Arabidopsis thaliana (L.) Heynh

Cadmium (Cd), one of the most widespread and water-soluble polluting heavy metals, has been widely studied on plants, even if the mechanisms underlying its phytotoxicity remain elusive. Indeed, most experiments are performed using extensive exposure time to the toxicants, not observing the primary targets affected. The present work studied Cd effects on Arabidopsis thaliana (L.) Heynh’s root apical meristem (RAM) exposed for short periods (24 h and 48 h) to acute phytotoxic concentrations (100 and 150 µM). The effects were studied through integrated morpho-histological, molecular, pharmacological and metabolomic analyses, highlighting that Cd inhibited primary root elongation by affecting the meristem zone via altering cell expansion. Moreover, Cd altered Auxin accumulation in RAM and affected PINs polar transporters, particularly PIN2. In addition, we observed that high Cd concentration induced accumulation of reactive oxygen species (ROS) in roots, which resulted in an altered organization of cortical microtubules and the starch and sucrose metabolism, altering the statolith formation and, consequently, the gravitropic root response. Our results demonstrated that short Cd exposition (24 h) affected cell expansion preferentially, altering auxin distribution and inducing ROS accumulation, which resulted in an alteration of gravitropic response and microtubules orientation pattern.

Low-order fine roots of Picea asperata have different physiological mechanisms in response to seasonal freeze and freeze-thaw of soil.

Seasonal soil freezing (F) and freeze-thaw cycles (FTCs) are common natural phenomena in high latitude or altitude areas of the world, and seriously affect plant physiological processes. However, studies on the effect of soil F and FTCs on fine roots are less common, especially in subalpine coniferous forests of western Sichuan, China. We set up a controlled experiment in growth chambers to explore the effects of F and FTCs on low-order fine roots of Picea asperata and differential responses of first-order roots and the first three root orders (1st, 2nd and 3rd order roots combined as a unit). Soil F and FTCs resulted in serious damage to cell membranes and root vitality of low-order fine roots, accompanied by increased MDA content and O2 ·- production. FTCs had a stronger effect than F treatment. In turn, low-order fine roots are the unit that responds to cold stress. These roots had increased unsaturated fatty acid contents, antioxidant enzyme activities, osmolytes and plant hormones contents when acclimation to cold stress. The first-order roots were more sensitive to cold stress than the combined first three root orders for several processes (e.g. antioxidant enzymes, osmolytes and hormones) because of their specific structure and physiological activity. This study explains physiological differences in responses of fine roots of different root orders to seasonal soil freezing, which will improve the understanding of fine root heterogeneity and support agriculture and forest management.

The molecular conformation, but not disaggregation, of humic acid in water solution plays a crucial role in promoting plant development in the natural environment.

Many studies have shown the capacity of soil humic substances (HS) to improve plant growth in natural ecosystems. This effect involves the activation of different processes within the plant at different coordinated molecular, biochemical, and physiological levels. However, the first event triggered by plant root-HS interaction remains unclear. Some studies suggest the hypothesis that the interaction of HS with root exudates involves relevant modification of the molecular conformation of humic self-assembled aggregates, including disaggregation, which might be directly involved in the activation of root responses. To investigate this hypothesis, we have prepared two humic acids. A natural humic acid (HA) and a transformed humic acid obtained from the treatment of HA with fungal laccase (HA enz). We have tested the capacity of the two humic acids to affect plant growth (cucumber and Arabidopsis) and complex Cu. Laccase-treatment did not change the molecular size but increased hydrophobicity, molecular compactness and stability, and rigidity of HA enz. Laccase-treatment avoided the ability of HA to promote shoot- and root-growth in cucumber and Arabidopsis. However, it does not modify Cu complexation features. There is no molecular disaggregation upon the interaction of HA and HA enz with plant roots. The results indicate that the interaction with plant roots induced in both HA and laccase-treated HA (HA enz), changes in their structural features that showed higher compactness and rigidity. These events might result from the interaction of HA and HA enz with specific root exudates that can promote intermolecular crosslinking. In summary, the results indicate that the weakly bond stabilized aggregated conformation (supramolecular-like) of HA plays a crucial role in its ability to promote root and shoot growth. The results also indicate the presence of two main types of HS in the rhizosphere corresponding to those non-interacting with plant roots (forming aggregated molecular assemblies) and those produced after interacting with plant root exudates (forming stable macromolecules).

A multifaceted approach to reveal the very-fine root's response of Fagus sylvatica seedlings to different drought intensities.

How temperate trees respond to drier summers strongly depends on the drought susceptibility and the starch reserve of the very-fine roots (<0.5 mm in diameter). We performed morphological, physiological, chemical, and proteomic analyses on very-fine roots of Fagus sylvatica seedlings grown under moderate- and severe drought conditions. Moreover, to reveal the role of the starch reserves, a girdling approach was adopted to interrupt the flux of photosynthates toward the downstream sinks. Results show a seasonal sigmoidal growth pattern without evident mortality under moderate drought. After the severe-drought period, intact plants showed lower starch concentration and higher growth than those subjected to moderate drought, highlighting that very-fine roots rely on their starch reserves to resume growth. This behavior caused them to die with the onset of autumn, which was not observed under moderate drought. These findings indicated that extreme dry soil conditions are needed for significant root death in beech seedlings and that mortality mechanisms are defined within individual compartments. The girdling treatment showed that the physiological responses of very-fine roots to severe drought stress are critically related to the altered load or the reduced transport velocity of the phloem and that the changes in starch allocation critically alter the distribution of biomass. Proteomic evidence revealed that the phloem flux-dependent response was characterized by the decrease of carbon enzymes and the establishment of mechanisms to avoid the reduction of the osmotic potential. The response independent from the aboveground mainly involved the alteration of primary metabolic processes and cell wall-related enzymes.

Key Pathways and Genes of Arabidopsis thaliana and Arabidopsis halleri Roots under Cadmium Stress Responses: Differences and Similarities.

Cadmium (Cd) is among the world's major health concerns, as it renders soils unsuitable and unsafe for food and feed production. Phytoremediation has the potential to remediate Cd-polluted soils, but efforts are still needed to develop a deep understanding of the processes underlying it. In this study, we performed a comprehensive analysis of the root response to Cd stress in A. thaliana, which can phytostabilize Cd, and in A. halleri, which is a Cd hyperaccumulator. Suitable RNA-seq data were analyzed by WGCNA to identify modules of co-expressed genes specifically associated with Cd presence. The results evidenced that the genes of the hyperaccumulator A. halleri mostly associated with the Cd presence are finely regulated (up- and downregulated) and related to a general response to chemical and other stimuli. Additionally, in the case of A. thaliana, which can phytostabilize metals, the genes upregulated during Cd stress are related to a general response to chemical and other stimuli, while downregulated genes are associated with functions which, affecting root growth and development, determine a deep modification of the organ both at the cellular and physiological levels. Furthermore, key genes of the Cd-associated modules were identified and confirmed by differentially expressed gene (DEG) detection and external knowledge. Together, key functions and genes shed light on differences and similarities among the strategies that the plants use to cope with Cd and may be considered as possible targets for future research.

The Role of IAA in Regulating Root Architecture of Sweetpotato (Ipomoea batatas [L.] Lam) in Response to Potassium Deficiency Stress.

Plants can adapt to the spatial heterogeneity of soil nutrients by changing the morphology and architecture of the root system. Here, we explored the role of auxin in the response of sweetpotato roots to potassium (K+) deficiency stress. Two sweetpotato cultivars, Xushu 32 (low-K-tolerant) and Ningzishu 1 (low-K-sensitive), were cultured in low K+ (0.1 mmol L-1, LK) and normal K+ (10 mmol L-1, CK) nutrient solutions. Compared with CK, LK reduced the dry mass, K+ content, and K+ accumulation in the two cultivars, but the losses of Xushu 32 were smaller than those of Ningzishu 1. LK also affected root growth, mainly impairing the length, surface area, forks number, and crossings number. However, Xushu 32 had significantly higher lateral root length, density, and surface area than Ningzishu 1, closely related to the roots' higher indole-3-acetic acid (IAA) content. According to the qPCR results, Xushu 32 synthesized more IAA (via IbYUC8 and IbTAR2) in leaves but transported and accumulated in roots through polar transport (via IbPIN1, IbPIN3, and IbAUX1). It was also associated with the upregulation of auxin signaling pathway genes (IbIAA4 and IbIAA8) in roots. These results imply that IAA participates in the formation of lateral roots and the change in root architecture during the tolerance to low K+ stress of sweetpotato, thus improving the absorption of K+ and the formation of biomass.

Regulation of the iron-deficiency response by IMA/FEP peptide.

Iron (Fe) is an essential micronutrient for plant growth and development, participating in many significant biological processes including photosynthesis, respiration, and nitrogen fixation. Although abundant in the earth's crust, most Fe is oxidized and difficult for plants to absorb under aerobic and alkaline pH conditions. Plants, therefore, have evolved complex means to optimize their Fe-acquisition efficiency. In the past two decades, regulatory networks of transcription factors and ubiquitin ligases have proven to be essential for plant Fe uptake and translocation. Recent studies in Arabidopsis thaliana (Arabidopsis) suggest that in addition to the transcriptional network, IRON MAN/FE-UPTAKE-INDUCING PEPTIDE (IMA/FEP) peptide interacts with a ubiquitin ligase, BRUTUS (BTS)/BTS-LIKE (BTSL). Under Fe-deficient conditions, IMA/FEP peptides compete with IVc subgroup bHLH transcription factors (TFs) to interact with BTS/BTSL. The resulting complex inhibits the degradation of these TFs by BTS/BTSL, which is important for maintaining the Fe-deficiency response in roots. Furthermore, IMA/FEP peptides control systemic Fe signaling. By organ-to-organ communication in Arabidopsis, Fe deficiency in one part of a root drives the upregulation of a high-affinity Fe-uptake system in other root regions surrounded by sufficient levels of Fe. IMA/FEP peptides regulate this compensatory response through Fe-deficiency-triggered organ-to-organ communication. This mini-review summarizes recent advances in understanding how IMA/FEP peptides function in the intracellular signaling of the Fe-deficiency response and systemic Fe signaling to regulate Fe acquisition.

Comparative transcriptomic and proteomic analyses of midrib and root of Wanjincheng orange (Citrus sinensis Osbeck) in response to the early invasion of Candidatus Liberibacter asiaticus

Citrus Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas), is the most destructive disease of citrus plant. HLB can harm almost all citrus varieties and no cure is currently available. Our previous study reported that Wanjincheng orange (Citrus sinensis Osbeck) leaf and root exhibit significant difference in response to CLas infection using leaf-disk grafting. In this study, we used a multiomic approach (proteomics and transcriptomics) to identify nodes that can help in explaining these differences and ultimately contribute to the understanding of the response of midrib and root in the early invasion of CLas. The results of comparative transcriptomic analysis displayed that 2,782 differentially expressed genes (DEGs) were upregulated and 2,807 were downregulated. Meanwhile, the results of comparative proteomic analysis displayed that 226 and 182 differentially expressed proteins (DEPs) were up- and downregulated by CLas, respectively. Transcriptomic and proteomic association analyses revealed 2 downregulated and 6 upregulated genes in midrib and root. The analysis of DEGs and DEPs revealed that secondary metabolites, and detoxification pathways played important roles in response to the early invasion of CLas. Moreover, nitrogen metabolism in midrib and root was influenced by CLas. This study revealed the transcriptomic and proteomic differences between midrib and root in Wanjincheng orange during early invasion of CLas and provided some potential genes and proteins for breeding HLB-tolerant citrus in future.

ASSESSING THE IMPACT OF INDOLE-3-BUTYRIC ACID (IBA) ON ROOTING EFFICIENCY IN CARNATION (DIANTHUS CARYOPHYLLUS L.) PROPAGATION UNDER PROTECTED CONDITIONS

The study aimed to assess the impact of varying Indole-3-Butyric Acid (IBA) concentrations on the rooting efficacy of Carnation (Dianthus Caryophyllus L.) cuttings within a controlled greenhouse setting. Different concentrations of IBA were applied to selected Carnation cultivars to stimulate root development. The greenhouse environment maintained controlled conditions, regulating temperature, humidity, and light to mimic optimal growth settings. The study focused on observing and analyzing rooting responses, particularly concerning root initiation, elongation, and biomass accumulation. Results indicated a distinct relationship between IBA concentrations and the rooting efficiency of Carnation cuttings. Lower concentrations displayed negligible effects on root development, while moderate concentrations significantly stimulated root initiation and elongation. Surprisingly, excessively high IBA concentrations led to reduced rooting responses, suggesting a hormetic effect on root growth. Morphological assessments highlighted that optimal IBA concentrations fostered vigorous root systems characterized by increased length, number, and mass of roots. This research underscores the pivotal role of precise IBA application in promoting successful rooting of Carnation cuttings, especially in controlled environments. The findings provide crucial insights for refining propagation techniques tailored specifically for Carnations, offering guidance to growers in optimizing IBA concentrations for efficient and sustainable cultivation practices in the floriculture industry. Further investigations delving into the prolonged impacts of IBA on overall plant growth and development would deepen the understanding derived from these findings.

Phosphorus management is key to effective deployment of root ideotypes in complex soil environments

PurposeWe questioned how root ideotypes selected for deep or shallow root architecture function in complex environments with heterogeneous distributions of phosphorus (P), such as in many cropping systems in north-eastern Australia.MethodsWe used the rhizobox method to evaluate how contrasting genotypes of durum wheat and sorghum (wide and narrow root angle) responded to combinations of starter-P and deep P bands.ResultsAlthough we found evidence that root angle may influence spatio-temporal exploration for deep P bands, (early) plant access to P was the critical driver for plant growth. Without P, root system growth was retarded such that genotypic differences were hardly observed. Access to P boosted root exploration at depth by virtue of greater root system size, such that wide-angle genotypes with P outperformed narrow-angle ones without P. Plastic root responses to P benefited the expression of the broader root system architecture. We observed variation between species and individual parameters, but overall Starter-P and deep P bands tended to deliver complementary benefits when considering plant growth, P uptake, and phenological development together.ConclusionOur study highlights that nutritional constraints may limit the ability of root ideotypes to function in complex target environments. Development and deployment of root ideotypes should consider how local conditions (including soil nutrient distribution, physical and biological properties) influence crop phenotype and their ability to deliver the intended benefits. Within this, soil nutrient management is a critical determinant and an opportunity to influence the target environment.