Adventitious Root Development Research Articles

Comprehensive transcriptome analysis unravels the crucial genes during adventitious root development induced by carbon monoxide in Cucumis sativus L.

Carbon monoxide (CO) has been reported to be participated in adventitious rooting. However, knowledge about the interrelationship between CO and phytohormones during rooting is obscure. The molecular mechanism of CO-induced rooting is currently unclear. The roles of CO in adventitious rooting in Cucumis sativus L. at the transcriptional level were investigated. The results show that 10μM hematin (a CO donor) has a significant positive effect on adventitious rooting in cucumber. A total of 1792 differentially expressed genes (DEGs; 1103 up-regulated and 689 down-regulated) were identified in hematin treatment by RNA sequencing analysis. There were 37, 18 and 19 DEGs significantly enriched in plant hormone signal transduction, sucrose and starch metabolism, and phenylalanine metabolism, respectively. Both transcriptome and real-time quantitative PCR results showed that the expressions of AUX22D, IAA6, SAUR21, SAUR24, GH3.5, CYCD3-3, TIFY10a, TIFY10A and TIF9 promoted the accumulation of IAA, BR, JA and SA in plant hormone signal transduction. The up-regulation of HK3, TPPF, otsB, TPS7, TPS9 and the down-regulation of AGPS1, AGPS3 increased the content of starch and total sugar by mediating the activity of some critical enzymes, including HK, TPS, TPP and AGP. PER47, PER61, PER24, PER66, PER4 and CCR2 increased the lignin content. Our results suggest that CO could promote the accumulation of plant hormones, starch, sugar and lignin during adventitious rooting by regulating the expression of some related genes, including AUX22D, IAA6, SAUR21, SAUR24, GH3.5, CYCD3-3, TIFY10a, TIFY10A, TIF9 HK3, otsB, TPS7, TPS9, AGPS1, AGPS3, PER47, PER61, PER24, PER66, PER4, and CCR2. Thus, we provides an interesting candidate gene list for further studies on the molecular mechanisms of adventitious rooting.

Genetic and Hormonal Blueprint of Shoot-Borne Adventitious Root Development in Rice and Maize.

The evolution of root architecture in plants was a prerequisite for the absorption of water and minerals from the soil, and thus a major determinant of terrestrial plant colonization. Cereals have a remarkably complex root system consisting of embryonic primary roots and post-embryonic lateral roots and shoot-borne adventitious roots. Among grass species, rice adventitious roots (also called crown roots) are developed from compressed nodes at the stem base, whereas in maize, besides crown roots, several aboveground brace roots are also formed, thus adventitious root types display species-specific diversity. Despite being the backbone for the adult root system in monocots, adventitious roots are the least studied of all the plant organs. In recent times, molecular genetics, genomics and proteomics-based approaches have been utilized to dissect the mechanism of post-embryonic meristem formation and tissue patterning. Adventitious root development is a cumulative effect of the actions and interactions of crucial genetic and hormonal regulators. In this review, we provide a comprehensive view of the key regulators involved during the different stages of adventitious root development in two important crop plants, rice and maize. We have reviewed the roles of major phytohormones, microRNAs and transcription factors and their crosstalk during adventitious root development in these cereal crops.

Differential Gene Expression and Withanolides Biosynthesis During in vitro and ex vitro Growth of Withania somnifera (L.) Dunal.

Ashwagandha (Withania somnifera L. Dunal) is a medicinally important plant with withanolides as its major bioactive compounds, abundant in the roots and leaves. We examined the influence of plant growth regulators (PGRs) on direct organogenesis, adventitious root development, withanolide biosynthetic pathway gene expression, withanolide contents, and metabolites during vegetative and reproductive growth phases under in vitro and ex vitro conditions. The highest shooting responses were observed with 6-benzylaminopurine (BAP) (2.0 mg L–1) + Kinetin (KIN) (1.5 mg L–1) supplementation. Furthermore, BAP (2.0 mg L–1) + KIN (1.5 mg L–1) + gibberellic acid (GA3) (0.5 mg L–1) exhibited better elongation responses with in vitro flowering. Half-strength MS medium with indole-3-butyric acid (IBA) (1.5 mg L–1) exhibited the highest rooting responses and IBA (1.0 mg L–1) with highest fruits, and overall biomass. Higher contents of withaferin A (WFA) [∼8.2 mg g–1 dry weight (DW)] were detected in the reproductive phase, whereas substantially lower WFA contents (∼1.10 mg g–1 DW) were detected in the vegetative phase. Cycloartenol synthase (CAS) (P = 0.0025), sterol methyltransferase (SMT) (P = 0.0059), and 1-deoxy-D-xylulose-5-phosphate reductase (DXR) (P = 0.0375) genes resulted in a significant fold change in expression during the reproductive phase. The liquid chromatography-mass spectrometry (LC-MS) analysis revealed metabolites that were common (177) and distinct in reproductive (218) and vegetative (167) phases. Adventitious roots cultured using varying concentrations of indole-3-acetic acid (IAA) (0.5 mg L–1) + IBA (1.0 mg L–1) + GA3 (0.2 mg L–1) exhibited the highest biomass, and IAA (0.5 mg L–1) + IBA (1.0 mg L–1) exhibited the highest withanolides content. Overall, our findings demonstrate the peculiarity of withanolide biosynthesis during distinct growth phases, which is relevant for the large-scale production of withanolides.

A simple, rapid, and quantifiable system for studying adventitious root formation in grapevine

Woody cutting is customarily utilized as a material in research on grape adventitious root formation (ARF). However, phenotypic heterogeneity caused by the complex background influenced its use for molecular mechanism research of ARF of grape. The present study tested various types of explants from grape tissue culture plantlets and found that the whole leaf: blade with the petiole (LP) was the simplest unit that can easily form adventitious roots (ARs). LP explants which can be easily obtained, directly generate ARs via de novo organogenesis from the base of the petiole. Plantlet age, node position, blade size, the health condition of leaves, and light intensity have been demonstrated to affect the homogeneity of the ARF phenotype in LP. By controlling these parameters, selected LPs cultured on a medium with 6 g·L-1 agar and 10 g·L-1 sucrose under dark conditions started rooting at 6–7 days after culture (DAC) and reached 100% rooting rate within 13–14 DAC. Using this system, the core role of auxin on ARF was verified by exogenous application of indole butyric acid (IBA) and N-1-naphthylphthalamic acid (NPA). Strikingly, we found that light promoted ARF in the absence of sucrose, but inhibited ARF in the presence of sucrose (10 g·L-1), while a low concentration of 0.34 µM NPA partially relieved the inhibition. Finally, this study confirmed that exogenous plant growth regulators (PGRs), including 6-benzyl aminopurine (6-BA), gibberellic acid 3 (GA3), and 2,4-epibrassinolide (EBR), significantly inhibited ARF. This simple, rapid, quantifiable ARF research system provides a new approach to studying the factors influencing the formation and development of grape adventitious roots and establishes a framework for investigating the mechanism of grape adventitious root induction and initiation.

Genome-wide identification of WOX gene family in apple and a functional analysis of MdWOX4b during adventitious root formation

The plant-specific WUSCHEL-related homeobox (WOX) genes are crucial for plant growth and development. Here, we systematically identified the MdWOX gene family in apple at the genome-wide level, and analyzed the phylogenetic relationships, conserved motifs, gene structure, and syntenic relationships of the MdWOX genes. A total of 18 MdWOX genes were identified and phylogenetic analysis placed them into three clades. The phylogenetic relationships among the WOXs were further supported by the analyses of gene structure and conserved motifs. Chromosomal distribution and synteny analysis revealed that whole-genome and segmental duplications have played key roles in MdWOX gene family expansion. Moreover, the MdWOX genes exhibit tissue-specific expression patterns and MdWOX4a, MdWOX4b, MdWOX5b, MdWOX11/12a, and MdWOX11/12b may play essential roles in adventitious root development. The adventitious rooting ability was enhanced in MdWOX4b transgenic tobacco lines. The results of this study provide useful information for future functional studies on MdWOXs in the development of apple rootstocks.

Hydrogen Sulfide Promotes Adventitious Root Development in Cucumber under Salt Stress by Enhancing Antioxidant Ability.

As a gas signal molecule, hydrogen sulfide (H2S) can enhance plant stress resistance. Here, cucumber (Cucumis sativus ‘Xinchun NO. 4’) explants were used to investigate the role of H2S in adventitious root development under salt stress. The results show that sodium chloride (NaCl) at 10 mM produced moderate salt stress. The 100 µM sodium hydrosulfide (NaHS) treatment, a H2S donor, increased root number and root length by 38.37% and 66.75%, respectively, indicating that H2S effectively promoted the occurrence of adventitious roots in cucumber explants under salt stress. The results show that under salt stress, NaHS treatment reduced free proline content and increased the soluble sugar and soluble protein content during rooting. Meanwhile, NaHS treatment enhanced the activities of antioxidant enzymes [peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT)], increased the content of ascorbic (ASA) and glutathione (GSH), reduced the content of hydrogen peroxide (H2O2) and the rate of superoxide radical (O2−) production, and decreased relative electrical conductivity (REC) and the content of malondialdehyde (MDA). However, the NaHS scavenger hypotaurine (HT) reversed the above effects of NaHS under salt stress. In summary, H2S promoted adventitious root development under salt stress through regulating osmotic substance content and enhancing antioxidant ability in explants.

Effects of Auxin (Indole-3-butyric Acid) on Adventitious Root Formation in Peach-Based Prunus Rootstocks.

Several Prunus species are among the most important cultivated stone fruits in the Mediterranean region, and there is an urgent need to obtain rootstocks with specific adaptations to challenging environmental conditions. The development of adventitious roots (ARs) is an evolutionary mechanism of high relevance for stress tolerance, which has led to the development of environmentally resilient plants. As a first step towards understanding the genetic determinants involved in AR formation in Prunus sp., we evaluated the rooting of hardwood cuttings from five Prunus rootstocks (Adafuel, Adarcias, Cadaman, Garnem, and GF 677) grown in hydroponics. We found that auxin-induced callus and rooting responses were strongly genotype-dependent. To investigate the molecular mechanisms involved in these differential responses, we performed a time-series study of AR formation in two rootstocks with contrasting rooting performance, Garnem and GF 677, by culturing in vitro microcuttings with and without auxin treatment (0.9 mg/L of indole-3-butyric acid [IBA]). Despite showing a similar histological structure, Garnem and GF677 rootstocks displayed dynamic changes in endogenous hormone homeostasis involving metabolites such as indole-3-acetic acid (IAA) conjugated to aspartic acid (IAA-Asp), and these changes could explain the differences observed during rooting.

Molecular basis of differential adventitious rooting competence in poplar genotypes.

Recalcitrant adventitious root (AR) development is a major hurdle in propagating commercially important woody plants. Although significant progress has been made to identify genes involved in subsequent steps of AR development, the molecular basis of differences in apparent recalcitrance to form AR between easy-to-root and difficult-to-root genotypes remains unknown. To address this, we generated cambium tissue-specific transcriptomic data from stem cuttings of hybrid aspen, T89 (difficult-to-root) and hybrid poplar OP42 (easy-to-root), and used transgenic approaches to verify the role of several transcription factors in the control of adventitious rooting. Increased peroxidase activity was positively correlated with better rooting. We found differentially expressed genes encoding reactive oxygen species scavenging proteins to be enriched in OP42 compared with T89. A greater number of differentially expressed transcription factors in cambium cells of OP42 compared with T89 was revealed by a more intense transcriptional reprograming in the former. PtMYC2, a potential negative regulator, was less expressed in OP42 compared with T89. Using transgenic approaches, we demonstrated that PttARF17.1 and PttMYC2.1 negatively regulate adventitious rooting. Our results provide insights into the molecular basis of genotypic differences in AR and implicate differential expression of the master regulator MYC2 as a critical player in this process.

Influence of treatment on rooting of arctic Salix species cuttings for revegetation

ABSTRACT Increased northern exploration and resource extraction highlight a need for effective revegetation techniques to restore disturbed environments. This study assessed effects of indole-3-butyric acid (IBA), water extracts of Salix and smoke, soaking time, and collection time on adventitious and lateral root development of Salix species cuttings collected from Diavik Diamond Mine Inc., Northwest Territories. Over 80 percent of fall and spring cuttings developed adventitious roots, yet only 30 percent of summer cuttings rooted, indicating strong seasonal influences. Many cuttings developed extensive root system architecture in 60 days; some developed up to six orders of roots. Root length decreased with increasing root order in all seasons, and season influenced length within root orders. Application of IBA increased number of primary roots per cutting per season and number of cuttings with less than fifty secondary roots per primary root. Longer soaking times increased number of primary roots per cutting in different seasons, and soaking up to ten days increased longest root length. Salix and smoke water extract applications increased number of cuttings with twenty-five to seventy-four secondary roots. This research highlights the importance of treatment effects on adventitious and lateral root development to optimize root system architecture of cuttings from northern shrub species.

Adventitious rooting and anatomical aspects of Campomanesia phaea stems

Current literature is lacking regarding the vegetative propagation of the cambuci tree (Campomanesia phaea O. Berg Landrum). This study aimed to verify the efficiency of cutting techniques via the assessment of cuttings of varying types and sizes, sampling dates, and the influence of treatments containing plant growth regulator indolebutyric acid (IBA) combined with the antioxidant ascorbic acid across different immersion times. The species was found not to develop adventitious roots easily, and hence, the herbaceous and woody stem materials were subjected to histochemical studies to elucidate their anatomical and physiological processes. To this end, plant material was polymerized in glycol methacrylate resin, cut into sections, and stained using toluidine blue (0.05%) or via histochemical staining with PAS/naphthol blue black. Anatomical analysis of plant structures revealed the presence of phenolic compounds and sclerenchyma tissue, which in turn are expected to negatively impact the development of adventitious roots.

Dissecting the Root Phenotypic and Genotypic Variability of the Iowa Mung Bean Diversity Panel.

Mung bean [Vigna radiata (L.) Wilczek] is a drought-tolerant, short-duration crop, and a rich source of protein and other valuable minerals, vitamins, and antioxidants. The main objectives of this research were (1) to study the root traits related with the phenotypic and genetic diversity of 375 mung bean genotypes of the Iowa (IA) diversity panel and (2) to conduct genome-wide association studies of root-related traits using the Automated Root Image Analysis (ARIA) software. We collected over 9,000 digital images at three-time points (days 12, 15, and 18 after germination). A broad sense heritability for days 15 (0.22–0.73) and 18 (0.23–0.87) was higher than that for day 12 (0.24–0.51). We also reported root ideotype classification, i.e., PI425425 (India), PI425045 (Philippines), PI425551 (Korea), PI264686 (Philippines), and PI425085 (Sri Lanka) that emerged as the top five in the topsoil foraging category, while PI425594 (unknown origin), PI425599 (Thailand), PI425610 (Afghanistan), PI425485 (India), and AVMU0201 (Taiwan) were top five in the drought-tolerant and nutrient uptake “steep, cheap, and deep” ideotype. We identified promising genotypes that can help diversify the gene pool of mung bean breeding stocks and will be useful for further field testing. Using association studies, we identified markers showing significant associations with the lateral root angle (LRA) on chromosomes 2, 6, 7, and 11, length distribution (LED) on chromosome 8, and total root length-growth rate (TRL_GR), volume (VOL), and total dry weight (TDW) on chromosomes 3 and 5. We discussed genes that are potential candidates from these regions. We reported beta-galactosidase 3 associated with the LRA, which has previously been implicated in the adventitious root development via transcriptomic studies in mung bean. Results from this work on the phenotypic characterization, root-based ideotype categories, and significant molecular markers associated with important traits will be useful for the marker-assisted selection and mung bean improvement through breeding.

Salicylic Acid Enhances Adventitious Root and Aerenchyma Formation in Wheat under Waterlogged Conditions.

The present study investigated the role of salicylic acid (SA) in regulating morpho-anatomical adaptive responses of a wheat plant to waterlogging. Our pharmacological study showed that treatment of waterlogged wheat plants with exogenous SA promotes the formation axile roots and surface adventitious roots that originate from basal stem nodes, but inhibits their elongation, leading to the formation of a shallow root system. The treatment also enhanced axile root formation in non-waterlogged plants but with only slight reductions in their length and branch root formation. Exogenous SA enhanced the formation of root aerenchyma, a key anatomical adaptive response of plants to waterlogging. Consistent with these results, waterlogging enhanced SA content in the root via expression of specific isochorismate synthase (ICS; ICS1 and ICS2) and phenylalanine ammonia lyase (PAL; PAL4, PAL5 and PAL6) genes and in the stem nodes via expression of specific PAL (PAL5 and PAL6) genes. Although not to the same level observed in waterlogged plants, exogenous SA also induced aerenchyma formation in non-waterlogged plants. The findings of this study furthermore indicated that inhibition of ethylene synthesis in SA treated non-waterlogged and waterlogged plants does not have any effect on SA-induced emergence of axile and/or surface adventitious roots but represses SA-mediated induction of aerenchyma formation. These results highlight that the role of SA in promoting the development of axile and surface adventitious roots in waterlogged wheat plants is ethylene independent while the induction of aerenchyma formation by SA requires the presence of ethylene.

Transcriptomic analyses provide insight into adventitious root formation of Euryodendron excelsum H. T. Chang during ex vitro rooting

Euryodendron excelsum H. T. Chang, a critically endangered species endemic to China, is a source of valuable material for the furniture and construction industries. However, this species has some challenges associated with rooting during in vitro propagation that have yet to be resolved. In this study, we optimized rooting and conducted a transcriptomic analysis to appreciate its molecular mechanism, thereby promoting the practical application of in vitro propagation of E. excelsum, and providing technical support for the ecological protection of this rare and endangered species. Results showed that ex vitro rooting performed the highest rooting percentage with 98.33% at 25 days. During ex vitro rooting, there was a wide fluctuation of endogenous levels of indole-3-acetic acid (IAA) and hydrogen peroxide (H2O2) at the stage of root primordia formation. Transcriptome analysis revealed multiple differentially expressed genes (DEGs) involved in adventitious root (AR) development. DEGs involved in plant hormone signal transduction, such as genes encoding auxin-induced protein, auxin-responsive protein, and auxin transporter-like protein, and in response to H2O2, oxidative stress, abiotic and biotic stimuli were significantly up- or down-regulated by ex vitro treatment with 1 mM indole-3-butyric acid (IBA). Our results indicate that ex vitro rooting is an effective method to induce AR from E. excelsum plantlets during micropropagation. DEGs involved in the plant hormone signal transduction pathway played a crucial role in AR formation. H2O2, produced by environmental stimulation, might be related to AR induction as a result of the synergistic action with IBA, ultimately regulating the level of endogenous IAA. Under ex vitro rooting, a synergistic action between H2O2 produced by environmental stimulation and IBA played crucial role in the regulation of AR formation from E. excelsum plantlets during micropropagation.

中华蚊母树在干旱-水淹交叉胁迫下形态和活性氧代谢的适应机制

PDF HTML阅读 XML下载 导出引用 引用提醒 中华蚊母树在干旱-水淹交叉胁迫下形态和活性氧代谢的适应机制 DOI: 10.5846/stxb202008062050 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（51779127）；国家111引智基地项目（D20015）；中国科学院水生植物与流域生态重点实验室开放课题基金（E0520204）；三峡库区珍稀植物种子保存技术与设施研究科研项目-耐水淹种质资源调查及收集（SDHZ2021346） Adaptive mechanism of morphology and reactive oxygen species metabolism of Distylium chinense seedlings to alternate drought and submergence stresses Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为阐明中华蚊母树（Distylium chinense）在消落带干旱-水淹交叉胁迫下的形态和活性氧（ROS）代谢适应机制，通过控制实验模拟了三峡水库消落带的水文节律，研究了干旱-水淹交叉胁迫及恢复过程施加不同外源物质对中华蚊母树形态学和ROS清除的变化。结果表明：（1）前期干旱胁迫增强了中华蚊母树对后期水淹胁迫的适应，主要表现在叶片脱落、大量不定根的形成及茎基部膨大等形态学的变化；（2）干旱或水淹单一胁迫下，中华蚊母树·OH、O2·等ROS水平明显高于对照，表现出氧化应激反应，其超氧化物歧化酶（SOD）、过氧化氢酶（CAT）、抗坏血酸过氧化物酶（APX）等抗氧化系统酶活性及脯氨酸（Pro）等抗氧化系统小分子含量也均显著高于对照，表现出一定的抗氧化防御作用机制，且在复合胁迫下，SOD、CAT、APX酶活性及Pro含量显著高于单一胁迫；（3）恢复阶段，相关性分析表明，中华蚊母树清除ROS （·OH、O2·）的酶促（SOD、CAT、APX）及非酶促（Pro）系统具有一定的协同性。同时，恢复阶段施加脱落酸（ABA），内源Pro显著高于正常水平；施加Pro，SOD、CAT等抗氧化酶活性显著高于对照；施加可溶性糖（Glu），APX活性显著升高。表明外源添加ABA、Pro、Glu，均对ROS的清除产生显著影响，同时，SOD活性显著高于CAT和APX活性，因此SOD可能是中华蚊母树清除冗余ROS的主要因子。因此，中华蚊母树形态学的变化、较高的脯氨酸积累和对ROS有效的清除防御，可能是其适应干旱-水淹交叉胁迫的主要机制，ABA、Pro、Glu等外源物质的添加对中华蚊母树的胁迫恢复过程具有显著的促进作用，前期干旱可提高中华蚊母树植株对后期水淹的耐受能力。 Abstract:Distylium chinense, the genus Distylium of the Hamamelidacea, is an evergreen perennial shrub between 0.8 and 1.2 m in height, native to the riparian areas and wetlands and a dominant species in the riparian areas of the Three Gorges Reservoir (TGR) region of the Yangtze River and its branches. Our previous studies showed that D. chinense had a certain survival rate in the middle and upper part of the water level fluctuation zone (WLFZ) of the TGR to alternate drought and submergence stresses, but the adaptive mechanisms of its morphology and reactive oxygen species (ROS) metabolism is still unknown. To evaluate its adaptation mechanisms of D. chinense to alternate drought and submergence stresses, a simulation alternate drought and submergence experiment was conducted, and morphology and ROS metabolism of D. chinense seedlings and their recovery growth with different exogenous substances, i.e., abscisic acid(ABA), proline(Pro) and glucose (Glu), were analyzed, including adventitious roots, plant height, base stem diameter, leaf numbers, ROS content, enzymatic and non-enzymatic antioxidant parameters. The results were as follows. (1) The early drought stress stimulated the adaptation of D. chinense seedlings to the later flooding stress.The adaptation mainly refered as more morphological changes of stems and roots i.e., stem base hypertrophy, formation and development of adventitious roots. (2) Comparing to the control group, there were significant increases in the ·OH and the O2· in D. chinense seedlings under either drought or flooding stress, which showed oxidative stress responses occurred and their superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities and the proline (Pro) contents were also significantly higher than those of controls, which showed that the enzymatic and non-enzymatic antioxidants were induced as a defense mechanism. Under the alternate drought and submergence stresses, the activities of SOD, APX and CAT and Pro contents were higher than those under single drought or flooding stress. (3) Correlation analysis showed that to a certain extent there were coordinated effects between the enzymatic (SOD, CAT, APX) and non-enzymatic (Pro) systems in ROS-scavenging in D. chinense. Exogenous ABA significantly triggered an increase of endogenous Pro contents compared to the controls during the recovery growth and the activity of SOD, CAT and APX was significantly higher than those of the control group under exogenous Pro treatment. Of these, the activities of SOD were significantly higher than those of CAT and APX. The activities of APX increased significantly when soluble sugar (Glu) was added. The ABA, Pro and Glu all had significant influences on the removal of ROS and the ability of D. chinense to up-regulate the SOD activity might be an important attribute for the removal of redundant ROS linked to drought and flooding tolerance. Thus the higher Pro accumulation and effective defense to ROS could be the main physiological adaptation mechanisms for D. chinense under the alternate drought and submergence stresses. The combination of morphological changes and the up-regulating of enzymatic and non-enzymatic anti-oxidative system might be the main mechanisms of D. chinense adapting to alternate drought and flooding stresses. The ABA, Pro and Glu treatment significantly promoted the recovery growth of D. chinense.. The drought in the early stage could improve the tolerance to submergence in the later stage. 参考文献 相似文献 引证文献

Loss of Gn1a/OsCKX2 confers heavy-panicle rice with excellent lodging resistance.

Significant achievements have been made in breeding programs for the heavy-panicle-type (HPT) rice (Oryza sativa) in Southwest China. The HPT varieties now exhibit excellent lodging resistance, allowing them to overcome the greater pressures caused by heavy panicles. However, the genetic mechanism of this lodging resistance remains elusive. Here, we isolated a major quantitative trait locus, Panicle Neck Diameter 1 (PND1), and identified the causal gene as GRAIN NUMBER 1A/CYTOKININ OXIDASE 2 (Gn1A/OsCKX2). The null gn1a allele from rice line R498 (gn1aR498 ) improved lodging resistance through increasing the culm diameter and promoting crown root development. Loss-of-function of Gn1a/OsCKX2 led to cytokinin accumulation in the crown root tip and accelerated the development of adventitious roots. Gene pyramiding between the null gn1aR498 allele with two gain-of-function alleles, STRONG CULM 2 (SCM2) and SCM3, further improved lodging resistance. Moreover, Gn1a/OsCKX2 had minimal influence on overall rice quality. Our research thus highlights the distinct genetic components of lodging resistance of HPT varieties and provides a strategy for tailor-made crop improvement of both yield and lodging resistance in rice.

Hypoxia tolerance of four millet species is attributable to constitutive aerenchyma formation and root hair development of adventitious roots

ABSTRACT The purpose was to elucidate the hypoxia tolerance mechanism of millet species by focusing on the oxygen acquisition mechanism of adventitious roots. Brachiaria ramosa, Echinochloa utilis, Eragrostis tef, and Setaria italica were used. Thirty-day old plants were hydroponically cultivated for 28 days as the control, where aeration was continued and a hypoxia treatment was applied, where nitrogen gas was flushed to reduce the oxygen concentration. From the stress susceptibility index based on plant growth rate, it was clarified that E. utilis and E. tef had higher hypoxia tolerance than B. ramosa and S. italica. Root growth rate, nitrogen concentration of leaves and stems, and sodium concentration per plant of the higher hypoxia-tolerant species did not change with hypoxia treatment. In hypoxia-susceptible millet species, the root growth rate and nitrogen concentration in the leaf and stem decreased, and the sodium concentration in the whole plant increased. The proportion of the stele area of the adventitious root of the hypoxia-tolerant millet species was smaller than that of the hypoxia-susceptible millet species, and the lysigenous aerenchyma was constitutively developed. Furthermore, root hairs were observed near the root tip in the hypoxia-tolerant millet species. In conclusion, we deduced that the hypoxia tolerance of the millet species is mainly attributable to the supply of oxygen to the root tip via the lysigenous aerenchyma along the adventitious root. Lower oxygen consumption by a smaller proportion of the stele area might be an important genetic trait. Furthermore, root hair may contribute to nutrient absorption.

The involvement of abscisic acid in glucose promoted adventitious root development in cucumber

Several lines of evidence suggest that glucose (Glc) and abscisic acid (ABA) are important signal molecules involved in plant growth and development. In the study, cucumber (Cucumis sativus ‘Xinchun NO. 4′) was used to understand the roles and relationships of Glc and ABA in adventitious root development. The results show that the effect of Glc and ABA on adventitious rooting in cucumber was dose-dependent, with a maximal biological response at 0.10 mM Glc and 0.05 μM ABA, respectively. However, the promotive roles of Glc in adventitious rooting were suppressed by ABA inhibitor fluridone (FLU), suggesting that endogenous ABA might be involved in Glc-induced adventitious rooting. Glc increased endogenous ABA content and the activity of ABA biosynthesis-related enzyme zeaxanthin epoxidase (ZEP), 9-cis-epoxy-carotenoid dioxigenase (NCED) and aldehyde oxidase (AO) during adventitious rooting. Glc decreased the activity of ABA degradation-related enzyme ABA 8′-hydroxylase (ABA8’-H). Glc significantly up-regulated the expression of ABA biosynthesis-related genes CsNCED1 and CsNCED2 and ABA signal transduction-related genes CsPYR1, CsPYR2, CsPYL8 and CsSRK2E, and significantly down-regulated the expression of ABA degradation-related genes CsCYP707A1 and CsCYP707A2. However, Glc-enhanced ABA content, ABA-related enzyme activity and ABA-related gene expression were reversed by FLU. Therefore, Glc might promote adventitious rooting by enhancing ABA accumulation, in which the activity of ABA biosynthesis enzyme (ZEP, NCED and AO), the expression of ABA biosynthesis-related genes (CsNCED1 and CsNCED2) and ABA signal transduction-related genes (CsPYR1, CsPYR2, CsPYL8 and CsSRK2E) were increased by Glc, and the activity of ABA degradation enzyme ABA8’-H and the expression of ABA degradation-related genes (CsCYP707A1 and CsCYP707A2) were inhibited by Glc.

The positive feedback regulatory loop of miR160-Auxin Response Factor 17-HYPONASTIC LEAVES 1 mediates drought tolerance in apple trees.

Drought stress tolerance is a complex trait regulated by multiple factors. Here, we demonstrate that the miRNA160-Auxin Response Factor 17 (ARF17)-HYPONASTIC LEAVES 1 module is crucial for apple (Malus domestica) drought tolerance. Using stable transgenic plants, we found that drought tolerance was improved by higher levels of Mdm-miR160 or MdHYL1 and by decreased levels of MdARF17, whereas reductions in MdHYL1 or increases in MdARF17 led to greater drought sensitivity. Further study revealed that modulation of drought tolerance was achieved through regulation of drought-responsive miRNA levels by MdARF17 and MdHYL1; MdARF17 interacted with MdHYL1 and bound to the promoter of MdHYL1. Genetic analysis further suggested that MdHYL1 is a direct downstream target of MdARF17. Importantly, MdARF17 and MdHYL1 regulated the abundance of Mdm-miR160. In addition, the Mdm-miR160-MdARF17-MdHYL1 module regulated adventitious root development. We also found that Mdm-miR160 can move from the scion to the rootstock in apple and tomato (Solanum lycopersicum), thereby improving root development and drought tolerance of the rootstock. Our study revealed the mechanisms by which the positive feedback loop of Mdm-miR160-MdARF17-MdHYL1 influences apple drought tolerance.

Corrigendum to: Genome-Wide Transcript Profiling Reveals an Auxin-Responsive Transcription Factor, OsAP2/ERF-40, Promoting Rice Adventitious Root Development

Corrigendum to: Genome-Wide Transcript Profiling Reveals an Auxin-Responsive Transcription Factor, OsAP2/ERF-40, Promoting Rice Adventitious Root Development

The transcription factor WRKY75 regulates the development of adventitious roots, lateral buds and callus by modulating hydrogen peroxide content in poplar.

Hydrogen peroxide (H2O2) plays important roles in plant development. Adventitious roots (AR), lateral buds (LB) and callus formation are important traits for plants. Here, a gene encoding RESPIRATORY BURST OXIDASE HOMOLOG B (PdeRBOHB) from poplar line 'NL895' (Populus. deltoides × P. euramericana) was predicted to be involved in H2O2 accumulation, and lines with reduced expression were generated. H2O2 content was decreased, and the development of adventitious roots, lateral buds, and callus was inhibited in reduced expression PdeRBOHB lines. A gene encoding PdeWRKY75 was identified as the upstream transcription factor positively regulating PdeRBOHB. This regulation was confirmed by dual luciferase reporter assay, GUS transient expression analysis and electrophoretic mobility shift assay. In the reduced expression PdeWRKY75 lines, H2O2 content was decreased and the development of adventitious roots, lateral buds, and callus development was inhibited, while in the overexpression lines, H2O2 content was increased and the development of adventitious roots and lateral buds was inhibited, but callus formation was enhanced. Additionally, reduced expression PdeRBOHB lines showed lowered expression of PdeWRKY75, while exogenous application of H2O2 showed the opposite effect. Together, these results suggest that PdeWRKY75 and PdeRBOHB are part of a regulatory module in H2O2 accumulation, which is involved in the regulation of multiple biological processes.