Summary
Flooding causes oxygen deprivation in soils. Plants adapt to low soil oxygen availability by changes in root morphology, anatomy, and architecture to maintain root system functioning. ...Essential traits include aerenchyma formation, a barrier to radial oxygen loss, and outgrowth of adventitious roots into the soil or the floodwater. We highlight recent findings of mechanisms of constitutive aerenchyma formation and of changes in root architecture. Moreover, we use modelling of internal aeration to demonstrate the beneficial effect of increasing cortex‐to‐stele ratio on sustaining root growth in waterlogged soils. We know the genes for some of the beneficial traits, and the next step is to manipulate these genes in breeding in order to enhance the flood tolerance of our crops.
See also the Editorial on this article by Sasidharan et al., 229: 5–7.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The interactions of NO and other signalling molecules contribute to adventitious root formation in many plant species. To our knowledge, the role of NO in the adventitious root formation of plants ...subjected to waterlogging are as yet unknown. Populations of Suaeda salsa L., a C3 euhalophytic plant, from inland saline sites develop several adventitious roots in response to waterlogging. The NO donor sodium nitroprusside (SNP) and the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1–1-oxyl-3-oxide (cPTIO) were applied to S. salsa seedlings to examine the effects of NO on flooding tolerance and its possible mechanism. SNP alleviated growth inhibition and increased adventitious root formation, endogenous NO levels and adventitious root cell integrity in S. salsa subjected to waterlogging. These SNP-mediated effects were prevented by the extra application of cPTIO. SNP treatment decreased nitrate reductase activity but increased nitric oxide synthase (NOS) activity in adventitious roots. These results suggest that in S. salsa, NO participates in waterlogging tolerance by enhancing adventitious root formation and that NO generation is associated with the NOS-associated pathway.
We review the detrimental effects of waterlogging on physiology, growth and yield of wheat. We highlight traits contributing to waterlogging tolerance and genetic diversity in wheat. Death of seminal ...roots and restriction of adventitious root length due to O2 deficiency result in low root:shoot ratio. Genotypes differ in seminal root anoxia tolerance, but mechanisms remain to be established; ethanol production rates do not explain anoxia tolerance. Root tip survival is short‐term, and thereafter, seminal root re‐growth upon re‐aeration is limited. Genotypes differ in adventitious root numbers and in aerenchyma formation within these roots, resulting in varying waterlogging tolerances. Root extension is restricted by capacity for internal O2 movement to the apex. Sub‐optimal O2 restricts root N uptake and translocation to the shoots, with N deficiency causing reduced shoot growth and grain yield. Although photosynthesis declines, sugars typically accumulate in shoots of waterlogged plants. Mn or Fe toxicity might occur in shoots of wheat on strongly acidic soils, but probably not more widely. Future breeding for waterlogging tolerance should focus on root internal aeration and better N‐use efficiency; exploiting the genetic diversity in wheat for these and other traits should enable improvement of waterlogging tolerance.
We review the detrimental effects of waterlogging on physiology, growth and yield of wheat, and we highlight traits contributing to waterlogging tolerance and genetic diversity in wheat. We use meta‐analyses based on published peer‐reviewed data to quantify the responses of wheat to waterlogging.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Acclimation of wheat to waterlogging is mediated by regulation of hormonal metabolism and transport in adventitious roots and during their emergence.
Abstract
To gain insights into the molecular ...mechanisms underlying hormonal regulation in adventitious roots and during their emergence under waterlogged conditions in wheat, the present study investigated transcriptional regulation of genes related to hormone metabolism and transport in the root and stem node tissues. Waterlogging-induced inhibition of axile root elongation and lateral root formation, and promotion of surface adventitious and axile root emergence and aerenchyma formation are associated with enhanced expression levels of ethylene biosynthesis genes, ACS7 and ACO2, in both tissues. Inhibition of axile root elongation is also related to increased root indole acetic acid (IAA) and jasmonate (JA) levels that are associated with up-regulation of specific IAA biosynthesis/transport (TDC, YUC1, and PIN9) and JA metabolism (LOX8, AOS1, AOC1, and JAR1) genes, and transcriptional alteration of gibberellin (GA) metabolism genes (GA3ox2 and GA2ox8). Adventitious root emergence from waterlogged stem nodes is associated with increased levels of IAA and GA but decreased levels of cytokinin and abscisic acid (ABA), which are regulated through the expression of specific IAA biosynthesis/transport (TDC, YUC1, and PIN9), cytokinin metabolism (IPT5-2, LOG1, CKX5, and ZOG2), ABA biosynthesis (NCED1 and NCED2), and GA metabolism (GA3ox2 and GA2ox8) genes. These results enhance our understanding of the molecular mechanisms underlying the adaptive response of wheat to waterlogging.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Unanticipated flooding challenges plant growth and fitness in natural and agricultural ecosystems. Here we describe mechanisms of developmental plasticity and metabolic modulation that underpin ...adaptive traits and acclimation responses to waterlogging of root systems and submergence of aerial tissues. This includes insights into processes that enhance ventilation of submerged organs. At the intersection between metabolism and growth, submergence survival strategies have evolved involving an ethylene-driven and gibberellin-enhanced module that regulates growth of submerged organs. Opposing regulation of this pathway is facilitated by a subgroup of ethylene-response transcription factors (ERFs), which include members that require low O2 or low nitric oxide (NO) conditions for their stabilization. These transcription factors control genes encoding enzymes required for anaerobic metabolism as well as proteins that fine-tune their function in transcription and turnover. Other mechanisms that control metabolism and growth at seed, seedling and mature stages under flooding conditions are reviewed, as well as findings demonstrating that true endurance of submergence includes an ability to restore growth following the deluge. Finally, wehighlight molecular insights obtained from natural variation of domesticated and wild species that occupy different hydrological niches, emphasizing the value of understanding natural flooding survival strategies in efforts to stabilize crop yields in flood-prone environments.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Melatonin (MT) is important for plant growth and development; however, it is not known whether MT is involved in apple adventitious root (AR) development. In this study, we treated Malus prunifolia ...(MP) at four different stages of AR development, and analyzed the level of the endogenous hormones MT, auxin (IAA), zeatin-riboside (ZR), abscisic acid (ABA), and gibberellins (GA
) in all four treatment groups and the untreated control group. The expression of MT, IAA biosynthesis, transport and signal transduction, the cell cycle, and root development related genes were quantified by RT-qPCR. The function of MdWOX11 was analyzed in transgenic apple plants.
The promotion of AR development by MT was dependent on the stage of AR induction between 0 and 2 d in apple rootstocks. MT-treatment increased the level of IAA and crosstalk existed between MT and IAA during AR formation. The expression of MdWOX11 was induced by MT treatment and positively regulated AR formation in apple. Furthermore, transgenic lines that overexpressed MdWOX11 lines produced more ARs than 'GL3'. Phenotypic analysis indicated that MdWOX11 overexpression lines were more sensitive to exogenous MT treatment than 'GL3', suggesting that MdWOX11 regulates AR formation in response to MT in apple rootstock.
MT promotes AR formation mainly during the AR induction stage by inducing IAA levels and upregulating MdWOX11.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•Black spruce trees formed continuous adventitious roots in water saturated soil.•Highest radial growth was registered in the younger adventitious roots.•Survival strategy: allocation of a higher ...amount of energy to the root system.
Large areas in boreal forests are classified as peatlands, characterized by organic soils with a high water table. Black spruce (Picea mariana (Mill.) B.S.P.) is one of the species capable of growing in this inauspicious environment, where an adaptation of the root system can be expected. We studied young black spruces growing in peat moss with two different hydrological conditions over a 19 years timespan: saturated and well-drained peat. We identified the initial and adventitious roots of the trees and compiled radial growth measurements of each root. The general growth pattern of the roots was identified and compared to the annual radial growth within the stem. We observed growth reductions during the first years after the planting shock, followed by a growth increase in the roots and stems for both hydrological conditions. The continuous formation of adventitious roots in trees growing in the saturated environment was the main adaptation noticed. The largest radial growth values were registered in the younger adventitious roots growing in saturated conditions. The lowest radial growth in the adventitious roots were registered in the well-drained condition. PCA analyses revealed the influence of root depth with regard to stem height and diameter at soil level. The black spruce trees displayed the required plasticity to form adventitious roots outside the range of the water table, allowing them a better access to oxygen and nutrients. This survival strategy implies to allocate a higher amount of energy to the root system instead of the aerial part of the tree in which overall productivity is low.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Reallocating root biomass from nodal roots to lateral and early-emerging axial roots allows maize to capture more nitrogen under limiting conditions, including by increasing foraging at depth.
...Abstract
Simulations indicated that reduced nodal root (NR) number (NRN) was promising for maize breeding, and were partially confirmed by relying on variation in NRN among inbreds. Using maize inbred line B73, experiments were conducted in hydroponics and tall mesocosms containing solid media with treatments involving no NR excision (0% NRE) or excising either 33% or 67% of the NRs as they emerged under high or low levels of nitrogen (N). Reduced NRN was hypothesized to increase elongation of all remaining root classes, N acquisition under low N, and shoot mass. Plants with 67% NRE had 12% and 19% less root mass fraction, 61% and 91% greater lateral to axial root length ratio regardless of N levels, and 61% and 182% greater biomass of embryonic roots under low N, compared with 0% NRE for hydroponics and mesocosms studies, respectively. Under low N in mesocosms, plants with 67% NRE had 52% greater shoot biomass, 450% greater root length at depth, and 232% greater deep-injected 15N content in the shoot relative to 0% NRE. These results reveal the mechanism by which plants with fewer NRs increase N capture and shoot mass by reallocation of biomass to lateral roots, embryonic roots, and first whorl NRs that increases foraging efficiency in solid media.
•Identified five miR160 members from miRBase of apple.•Cloned and analyzed the precursor sequence of five mdm-miR160 members in four apple rootstocks with different adventitious root generated ...ability.•Analyzed the expression pattern of miR160 and its target gene MdARF16 and MdARF17 in the four apple rootstocks.•Over-expressed mdm-miR160a in tobacco showed that it inhibited AR formation in transgenic lines, however exogenous indole-3-butyric acid (IBA) treatment could rescue the phenotype of AR formation in them.•The expression pattern of endogenous miRNA and its target gene in response to auxin in over-expressing mdm-miR160 tobacco was verified.
Adventitious root (AR) formation is an essential process for the vegetative propagation of apple rootstocks. However, the mechanisms of miR160 mediate AR formation in apple remains to be seen. In this study, five mdm-miR160 family members were identified in apple rootstocks and two AUXIN RESPONSIVE FACTOR (MdARF16 and MdARF17) were found as the targets of mdm-miR160. Furthermore, the sequences of mdm-miR160 family members’ precursors were cloned from four different AR rooting ability apple rootstocks, whereas, mdm-miR160a, mdm-miR160c and mdm-miR160e were highly conserved than mdm-miR160b and mdm-miR160d. Mdm-miR160 and their targets expression patterns showed obviously negative relationship in different stages during AR formation. In addition, the transcript level of mdm-miR160 was higher in ‘SH6’ and lower in ‘MP’, where it responds to exogenous indole-3-butyric acid (IBA). Mdm-miR160a was cloned from ‘M26’ and used for further experiments. The result of over-expressed mdm-miR160a in tobacco (Nicotiana tabacum L.cv.SR1) inhibited AR formation in 35S:MdMIR160a transgenic lines as compared with WT, whereas, exogenous IBA treatment could promote AR formation in 35S:MdMIR160a transgenic lines. Expression of five endogenous miRNAs: miR167c, miR393a, miR396a, miR396b, and miR156 in transgenic lines were lower than in WT. Moreover, the targets of endogenous miRNAs in transgenic lines showed different expression patterns with WT. In consistent, mdm-miR160 was an auxin responsive factor and participated in AR formation in apple rootstock, however, over-expressed mdm-miR160a has inhibitory effect on AR formation while exogenous IBA treatment could raise the rooting ability of transgenic lines.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
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