Maize leaf temperature responses to drought: Thermal imaging and quantitative trait loci (QTL) mapping

Leaf temperature has been shown to vary when plants are subjected to water stress conditions. Recent advances in infrared thermography have increased the probability of recording drought tolerant responses more accurately. The aims of this study were to identify the effects of drought on leaf temperature using infrared thermography. Furthermore, the genomic regions responsible for the expression of leaf temperature variation in maize seedlings (Zea mays L.) were explored. The maize inbred lines Zong3 and 87-1 were evaluated using infrared thermography and exhibited notable differences in leaf temperature response to water stress. Correlation analysis indicated that leaf temperature response to water stress played an integral role in maize biomass accumulation. Additionally, a mapping population of 187 recombinant inbred lines (RILs) derived from a cross between Zong3 and 87-1 was constructed to identify quantitative trait loci (QTL) responsible for physiological traits associated with seedling water stress. Leaf temperature differences (LTD) and the drought tolerance index (DTI) of shoot fresh weight (SFW) and shoot dry weight (SDW) were the traits evaluated for QTL analysis in maize seedlings. A total of nine QTL were detected by composite interval mapping (CIM) for the three traits (LTD, RSFW and RSDW). Two co-locations responsible for both RSFW and RSDW were detected on chromosomes 1 and 2, respectively, which showed common signs with their trait correlations. Another co-location was detected on chromosome 9 between LTD and shoot biomass, which provided genetic evidence that leaf temperature affects biomass accumulation. Additionally, the utility of a thermography system for drought tolerance breeding in maize was discussed.     

The role of miR156/SPLs modules in Arabidopsis lateral root development

miR156 is an evolutionarily highly conserved miRNA in plants that defines an age‐dependent flowering pathway. The investigations thus far have largely, if not exclusively, confined to plant aerial organs. Root branching architecture is a major determinant of water and nutrients uptake for plants. We show here that MIR156 genes are differentially expressed in specific cells/tissues of lateral roots. Plants overexpressing miR156 produce more lateral roots whereas reducing miR156 levels leads to fewer lateral roots. We demonstrate that at least one representative from the three groups of miR156 targets SQUAMOSA PROMOTER BINDING PROTEIN‐LIKE (SPL) genes: SPL3, SPL9 and SPL10 are involved in the repression of lateral root growth, with SPL10 playing a dominant role. In addition, both MIR156 and SPLs are responsive to auxin signaling suggesting that miR156/SPL modules might be involved in the proper timing of the lateral root developmental progression. Collectively, these results unravel a role for miR156/SPLs modules in lateral root development in Arabidopsis.     

Root responses of Quercus ilex L. seedlings to drought and fire

Abstract

Drought treatments in holm-oak (Quercus ilex) seedlings induce variations in total root length, number of root apices, shoot/root dry weight, and root electrolyte leakage. When drought treatments last for more than 50 days a considerable number of fine lateral roots die, irrespective of branching order or distribution within the root system. Scorching of drought-treated seedlings induces a transient stimulation of root growth. These results indicate that root turnover is deeply affected during treatments, with survival of seedlings being entrusted to the tolerance of a number of roots situated in the deeper region of the root system. Activity of the meristematic tissue present within the apices of these surviving roots supports regeneration of above-ground lost organs during recovery. Knowledge of the mechanisms ensuring the survival of Mediterranean tree seedlings following drought and fire is useful for developing models of vegetation dynamics.     

Maize root responses to drought stress depend on root class and axial position

In this study we tested the hypotheses that root classes would exhibit distinctive anatomical and architectural responses to drought stress, and that those responses would vary along the root axes. The root systems of four maize (Zea mays L.) sweet corn genotypes designated SC1, SC2, SC3 and SC4 were phenotyped under well-watered and drought treatments in greenhouse mesocosms, permitting increasing stratification of moisture availability as the drought progressed. Anatomical and architectural responses to drought were evaluated for each root class. Lignin distribution was assessed by image processing of UV-illuminated root cross-sections acquired by laser ablation tomography. The two cultivars with less biomass reduction under drought, SC3 and SC4, substantially enhanced lateral root development along the apical segments of axial roots when plants were grown with drought stress. These segments grew into the deeper part of the mesocosm where more moisture was available. Apical segments of the axial and large lateral roots from drought-stressed plants were thicker and had greater theoretical axial water conductance than basal segments, especially in SC3 and SC4. Basal segments of crown roots of SC3 and SC4 showed increased lignification of the stele under drought. Root anatomical and architectural responses to drought are complex and vary among cultivars and root classes, and along root axes. Drought-induced proliferation of lateral roots on apical segments of axial roots would be expected to enhance deep water acquisition, while lignification of axial roots could help preserve axial water transport.

     

Inhibition of primary roots and stimulation of lateral root development in Arabidopsis thaliana by the rhizobacterium Serratia marcescens 90–166 is through both auxin-dependent and -independent signaling pathways

The rhizobacterium Serratia marcescens strain 90–166 was previously reported to promote plant growth and induce resistance in Arabidopsis thaliana. In this study, the influence of strain 90-166 on root development was studied in vitro. We observed inhibition of primary root elongation, enhanced lateral root emergence, and early emergence of second order lateral roots after inoculation with strain 90–166 at a certain distance from the root. Using the DR5::GUS transgenic A. thaliana plant and an auxin transport inhibitor, N-1-naphthylphthalamic acid, the altered root development was still elicited by strain 90–166, indicating that this was not a result of changes in plant auxin levels. Intriguingly, indole-3-acetic acid, a major auxin chemical, was only identified just above the detection limit in liquid culture of strain 90–166 using liquid chromatography-mass spectrometry. Focusing on bacterial determinants of the root alterations, we found that primary root elongation was inhibited in seedlings treated with cell supernatant (secreted compounds), while lateral root formation was induced in seedlings treated with lysate supernatant (intracellular compounds). Further study revealed that the alteration of root development elicited by strain 90–166 involved the jasmonate, ethylene, and salicylic acid signaling pathways. Collectively, our results suggest that strain 90–166 can contribute to plant root development via multiple signaling pathways.     

Genetic variation in ZmTIP1 contributes to root hair elongation and drought tolerance in maize

Drought is a major abiotic stress that threatens maize production globally. A previous genome‐wide association study identified a significant association between the natural variation of ZmTIP1 and the drought tolerance of maize seedlings. Here, we report on comprehensive genetic and functional analysis, indicating that ZmTIP1, which encodes a functional S‐acyltransferase, plays a positive role in regulating the length of root hairs and the level of drought tolerance in maize. We show that enhancing ZmTIP1 expression in transgenic Arabidopsis and maize increased root hair length, as well as plant tolerance to water deficit. In contrast, ZmTIP1 transposon‐insertional mutants displayed the opposite phenotype. A calcium‐dependent protein kinase, ZmCPK9, was identified as a substrate protein of ZmTIP1, and ZmTIP1‐mediated palmitoylation of two cysteine residues facilitated the ZmCPK9 PM association. The results of this research enrich our knowledge about ZmTIP1‐mediated protein S‐acylation modifications in relation to the regulation of root hair elongation and drought tolerance. Additionally, the identification of a favourable allele of ZmTIP1 also provides a valuable genetic resource or selection target for the genetic improvement of maize.     

Reduced Soybean Water Stress Tolerance by miR393a-Mediated Repression of GmTIR1 and Abscisic Acid Accumulation

MicroRNA393 (miR393) has been shown to regulate plant water stress tolerance through an auxin signaling pathway. However, its role in soybean (Glycine max [L.] Merr.) has not yet been reported. Here, we examined the expression pattern of miR393 family members and their target gene GmTIR1 in water-stressed roots. Subsequently, we analyzed the functions of miR393 in the regulation of water stress tolerance and its relationship with GmTIR1 and abscisic acid (ABA) using a transgenic hairy root assay. Under water stress, miR393 family genes exhibited diverse expression patterns. Overexpression and knockdown analysis demonstrated that miR393a reduced water stress tolerance as measured by root vigor, net photosynthetic rate (Pn), and relative water content (RWC). Moreover, miR393a also caused down-regulation of GmTIR1A and GmTIR1B expression, an early decrease in hydrogen peroxide (H₂O₂) levels, early and late declines in ABA content and antioxidant activities, and a late elevation of H₂O₂ and malondialdehyde (MDA) concentrations in stressed hairy roots. However, overexpression and RNAi analyses showed that GmTIR1A and GmTIR1B triggered an early increase in H₂O₂, a rise in antioxidant activities during the early and late stages, a late decline in H₂O₂ and MDA contents, and a rise in root vigor, Pn, and RWC under water stress. Similarly, exogenously supplied ABA caused early H₂O₂ accumulation, early and late increases in antioxidant capacity, and a late decrease in oxidative damage in stressed miR393a-overexpressing roots. Therefore, our study presents a valuable model in which miR393a prevents early GmTIR1- and ABA-dependent increases in H₂O₂ and thus triggers a rise in antioxidant capacity, root vigor, RWC, and Pn, consequently decreasing water stress tolerance.

     

Potential role of D-<Emphasis Type="Italic">myo</Emphasis>-inositol-3-phosphate synthase and 14-3-3 genes in the crosstalk between <Emphasis Type="Italic">Zea mays</Emphasis> and <Emphasis Type="Italic">Rhizophagus intraradices</Emphasis> under drought stress

Arbuscular mycorrhizal (AM) symbiosis is known to stimulate plant drought tolerance. However, the mechanisms underlying the synergistic responses of the symbiotic partners to drought stress are largely unknown. A split-root experiment was designed to investigate the molecular interactions between a host plant and an AM fungus (AMF) under drought stress. In the two-compartment cultivation system, an entire or only a half root system of a maize plant was inoculated with an AMF, Rhizophagus intraradices, in the presence of localized or systemic drought treatment. Plant physiological parameters including growth, water status, and phosphorus concentration, and the expression of drought tolerance-related genes in both roots and R. intraradices were recorded. Although mycorrhizal inoculation in either one or both compartments systemically decreased abscisic acid (ABA) content in the whole root system subjected to systemic or local drought stress, we observed local and/or systemic AM effects on root physiological traits and the expression of functional genes in both roots and R. intraradices. Interestingly, the simultaneous increase in the expression of plant genes encoding D-myo-inositol-3-phosphate synthase (IPS) and 14-3-3-like protein GF14 (14-3GF), which were responsible for ABA signal transduction, was found to be involved in the activation of 14-3-3 protein and aquaporins (GintAQPF1 and GintAQPF2) in R. intraradices. These findings suggest that coexpression of IPS and 14-3GF is responsible for the crosstalk between maize and R. intraradices under drought stress, and potentially induces the synergistic actions of the symbiotic partners in enhancing plant drought tolerance.     

The impact of limited soil moisture and waterlogging stress conditions on morphological and anatomical root traits in maize (Zea mays L.) hybrids of different drought tolerance

Effects of soil drought or waterlogging on the morphological traits of the root system and internal root anatomy were studied in maize hybrids of different drought tolerance. The investigations comprised quantitative and qualitative analyses of a developed plant root system through determining the number, length and dry matter of the particular components of the root system and some traits of the anatomical structure of the seminal root. Obtained results have demonstrated a relatively broad variation in the habit of the root system. This mainly refers, to the number, length and dry matter of lateral roots, developed by seminal root, seminal adventitious and nodal roots as well as to some anatomical properties of the stele, cortex and metaxylem elements. Plants grown under waterlogging or drought conditions showed a smaller number and less dry matter of lateral branching than plants grown in control conditions. The harmful effect of waterlogging conditions on the growth of roots was greater when compared with that of plants exposed to drought. In the measurements of the root morphological traits, the effect of soil drought on the internal root anatomical characteristic was weaker than the effect of soil waterlogging. The observed effects of both treatments were more distinct in a drought sensitive hybrid Pioneer D than in drought resistant Pioneer C one. The drought resistant hybrid Pioneer C distinguished by a more extensive rooting and by smaller alterations in the root morphology caused by the stress conditions than drought sensitive hybrid Pioneer D one. Also the differences between the resistant and the sensitive maize hybrids were apparent for examined root anatomical traits. Results confirm that the hybrid Pioneer D of a high drought susceptibility was found to be also more sensitive to periodieal soil water excess. A more efficient water use and a lower shoot to root (S:R) ratio were found to be major reasons for a higher stress resistance of the hybrid Pioneer C. The reasons for a different response of the examined hybrids to the conditions of drought or waterlogging may be a more economical water balance and more favourable relations between the shoot and root dimensions in the drought resistant genotype. The observed modifications of the internal root structure caused by water deficit in plant tissues may partly influence on water conductivity and transport within roots. The results suggest that the morphological and anatomical traits of the maize root system may be used in practice as direct or indirect selection criteria in maize breeding.     

The peu‐miR160a−PeARF17.1/PeARF17.2 module participates in the adventitious root development of poplar

Deep roots give rise to flourishing leaves, and the two complement each other. However, the genetic mechanisms underlying adventitious rooting for forest trees have remained elusive. In this study, we verified that peu‐miR160a targets six poplar genes AUXIN RESPONSE FACTORS (ARFs), PeARF10.1, PeARF16.1, PeARF16.2, PeARF16.3, PeARF17.1 and PeARF17.2, using 5’RLM‐RACE. Interaction experiments with peu‐miR160a and PeARFs in poplar protoplasts further confirmed that peu‐miR160a targets and negatively regulates the six PeARFs. Peu‐miR160a and its target genes exhibited obvious temporal expression in different stages of adventitious root development, and they could also be induced by IAA and abscisic acid. Peu‐miR160a‐overexpressing lines exhibited a significant shortening of adventitious root length, an increase in the number of lateral roots, severe dwarfing and shortened internodes. In addition, the overexpression of PeARF17.1 or mPeARF17.2 (peu‐miR160a‐resistant version of PeARF17.2) significantly increased the number of adventitious roots. Furthermore, PeARF17.1‐overexpressing lines had multiple branches with no visible trunk, although the adventitious root length of the PeARF17.1‐overexpressing lines was significantly increased. Our findings reveal that the peu‐miR160a ? PeARF17.1/PeARF17.2 module is an important regulator involved in the development of the adventitious roots of poplar.     

QTLs for the elongation of axile and lateral roots of maize in response to low water potential

Changes in root architecture and the maintenance of root growth in drying soil are key traits for the adaptation of maize (Zea mays L.) to drought environments. The goal of this study was to map quantitative trait loci (QTLs) for root growth and its response to dehydration in a population of 208 recombinant inbred lines from the International Maize and Wheat Improvement Center (CIMMYT). The parents, Ac7643 and Ac7729/TZSRW, are known to be drought-tolerant and drought-sensitive, respectively. Roots were grown in pouches under well-watered conditions or at low water potential induced by the osmolyte polyethylene glycol (PEG 8000). Axile root length (L _Ax) increased linearly, while lateral root length (L _Lat) increased exponentially over time. Thirteen QTLs were identified for six seedling traits: elongation rates of axile roots (ER_Ax), the rate constant of lateral root elongation (k _Lat), the final respective lengths (L _Ax and L _Lat), and the ratios k _Lat/ER_Ax and L _Lat/L _Ax. While QTLs for lateral root traits were constitutively expressed, most QTLs for axile root traits responded to water stress. For axile roots, common QTLs existed for ER_Ax and L _Ax. Quantitative trait loci for the elongation rates of axile roots responded more clearly to water stress compared to root length. Two major QTLs were detected: a QTL for general vigor in bin 2.02, affecting most of the traits, and a QTL for the constitutive increase in k _Lat and k _Lat/ER_Ax in bins 6.04–6.05. The latter co-located with a major QTL for the anthesis-silking interval (ASI) reported in published field experiments, suggesting an involvement of root morphology in drought tolerance. Rapid seedling tests are feasible for elucidating the genetic response of root growth to low water potential. Some loci may even have pleiotropic effects on yield-related traits under drought stress.     

Root Morphology and Gene Expression Analysis in Response to Drought Stress in Maize (Zea mays)

Water-deficit stress tolerance is a complex trait, and water deficit results in various physiological and chemical changes in maize (Zea mays L.) and exacerbates pre-harvest aflatoxin contamination. The objective of this study was to characterize the variations in morphology, physiology, and gene expression in two contrasting inbred lines, Lo964 and Lo1016, in order to understand the differences in response to water-deficit stress. The results revealed that Lo964 was less sensitive to water-deficit stress, and had a strong lateral root system and a higher root/shoot ratio in comparison to Lo1016. In response to water-deficit stress by comparing stressed versus well-watered conditions, abscisic acid syntheses were increased in leaves, roots, and kernels of both Lo964 and Lo1016, but by different magnitudes. Indole-3-acetic acid (IAA) was undetectable in the leaves and roots of either genotype regardless of treatments, but increases of 58% and 8% in IAA concentration were observed in 20 DAP kernels, in response to water-deficit stress, respectively. The expression of the MIPS was up-regulated 7-fold in leaf tissues of Lo964 compared to Lo1016 at watered conditions, but decreased significantly to similar levels in both genotypes at water-deficit conditions. ZmPR10 and ZmFer1 expressions tended to up-regulate although ZmPR10 was expressed higher in root tissue while ZmFer1 was expressed higher in leaf tissue. Further study is needed to confirm if Lo964 has reduced aflatoxin contamination associated with the drought tolerance in the field in order to utilize the resistant trait in breeding.     

Early vertical distribution of roots and its association with drought tolerance in tropical maize

Background and aims

Selection for deep roots to improve drought tolerance of maize (Zea mays L.) requires presence of genetic variation and suitable screening methods.

Methods

We examined a diverse set of 33 tropical maize inbred lines that were grown in growth columns in the greenhouse up to the 2-, 4-, and 6-leaf stage and in the field in Mexico. To determine length of roots from different depths at high throughput, we tested an approach based on staining roots with methylene blue and measuring the amount of absorbed dye as proxy measure for root length.

Results

Staining provided no advantage over root weights that are much easier to measure and therefore preferable. We found significant genotypic variation for all traits at the 6-leaf stage. For development rates between the 2-leaf and the 6-leaf stage, genotypes only differed for rooting depth and the number of crown roots. Positive correlations of leaf area with root length and rooting depth indicated a common effect of plant vigor. However, leaf area in growth columns was negatively related to grain yield under drought (r?=??0.50).

Conclusion

The selection for deeper roots by an increase in plant vigor likely results in a poorer performance under drought conditions. The proportion of deep roots was independent of other traits but showed a low heritability and was not correlated to field performance. An improved screening protocol is proposed to increase throughput and heritability for this trait.

     

褪黑素对玉米幼苗根系发育和抗旱性的影响

褪黑素是一种在生物体内广泛存在的吲哚胺类化合物,参与植物的多种生理和生化过程.近年来研究认为褪黑素可以不同程度地增强植物的抗逆性,但对其作用机理仍知之甚少.通过两种褪黑素的施用方法,详细研究了褪黑素对于玉米根系发育和抗旱性的影响.首先,采用水培根灌褪黑素的方法对玉米幼苗的根系和生长状况进行分析,结果表明施加褪黑素显著提...     

Nitrogen enrichment lowers Betula pendula green and yellow leaf stoichiometry irrespective of effects of elevated carbon dioxide

Deep rooting has been identified as strategy for desiccation avoidance in natural vegetation as well as in crops like rice and sorghum. The objectives of this study were to determine root morphology and water uptake of four inbred lines of tropical maize (Zea mays L.) differing in their adaptation to drought. The specific questions were i) if drought tolerance was related to the vertical distribution of the roots, ii) whether root distribution was adaptive or constitutive, and iii) whether it affected water extraction, water status, and water use efficiency (WUE) of the plant. In the main experiment, seedlings were grown to the V5 stage in growth columns (0.80 m high) under well-watered (WW) and water-stressed (WS) conditions. The depth above which 95 % of all roots were located (D₉₅) was used to estimate rooting depth. It was generally greater for CML444 and Ac7729/TZSRW (P2) compared to SC-Malawi and Ac7643 (P1). The latter had more lateral roots, mainly in the upper part of the soil column. The increase in D₉₅ was accompanied by increases in transpiration, shoot dry weight, stomatal conductance and relative water content without adverse effects on the WUE. Differences in the morphology were confirmed in the V8 stage in large boxes: CML444 with thicker (0.14 mm) and longer (0.32 m) crown roots compared to SC-Malawi. Deep rooting, drought sensitive P2 showed markedly reduced WUE, likely due to an inefficient photosynthesis. The data suggest that a combination of high WUE and sufficient water acquisition by a deep root system can increase drought tolerance.

     

Rootless with undetectable meristem 1 encodes a monocot-specific AUX/IAA protein that controls embryonic seminal and post-embryonic lateral root initiation in maize

The maize (Zea mays L.) rum1‐R (rootless with undetectable meristems 1‐Reference) mutant does not initiate embryonic seminal roots and post‐embryonic lateral roots at the primary root. Map‐based cloning revealed that Rum1 encodes a 269 amino acid (aa) monocot‐specific Aux/IAA protein. The rum1‐R protein lacks 26 amino acids including the GWPPV degron sequence in domain II and part of the bipartite NLS (nuclear localization sequence). Significantly reduced lateral root density (approximately 35%) in heterozygous plants suggests that the rum1‐R is a semi‐dominant mutant. Overexpression of rum1‐R under the control of the maize MSY (Methionine SYnthase) promoter supports this notion by displaying a reduced number of lateral roots (31–37%). Functional characterization suggests that Rum1 is auxin‐inducible and encodes a protein that localizes to the nucleus. Moreover, RUM1 is unstable with a half life time of approximately 22 min while the mutant rum1‐R protein is very stable. In vitro and in vivo experiments demonstrated an interaction of RUM1 with ZmARF25 and ZmARF34 (Z. mays AUXIN RESPONSE FACTOR 25 and 34). In summary, the presented data suggest that Rum1 encodes a canonical Aux/IAA protein that is required for the initiation of embryonic seminal and post‐embryonic lateral root initiation in primary roots of maize.