Differential Gene Expression Between Wheat Hybrids and Their Parental Inbreds in Primary Roots

To provide an insight into the molecular basis of heterosis, differential display of mRNA was used to analyze the difference of gene expression between wheat (Triticum aestivum L.) heterotic hybrid A, nonheterotic hybrid B and their parental inbreds in the primary roots. By using 5′ end random primers in combination with three one-base-anchored primers, it was found that 22.5% and 22.9% of 877 total displayed cDNAs were differentially expressed between hybrid A, B and their parents, respectively. Both quantitative and qualitative differences in gene expression between hybrids and their parental inbreds were obvious, indicating that the patterns of gene expression in hybrids alter significantly as compared to their corresponding parents. On the other hand, by using MADS-box gene specific 5′ end primer for DDRT-PCR, we found that nearly all of the displayed cDNA fragments were polymorphic between hybrids and their parents, and major difference occurred in qualitative level, in which hybrid specific-expressed and silenced genes are the major two patterns, suggesting that MADS-box gene may be important for manifestation of differential gene expression and wheat heterosis. In comparison with our previous results by using seedling leaves, it is indicated that differential gene expression between hybrids and parents is dependent on the tissues tested, and more differentially expressed genes were observed in the primary roots than in the seedling leaves. Therefore, it is concluded that the expressions of both randomly displayed cDNAs and transcription factor genes, such as MADS-box, alter significantly between hybrids and their parents, which might be responsible for the observed heterosis.

Metabolic responses to combined water deficit and salt stress in maize primary roots

Soil water deficit and salt stress are major limiting factors of plant growth and agricultural productivity. The primary root is the first organ to perceive the stress signals for drought and salt stress. In this study, maize plant subjected to drought, salt and combined stresses displayed a significantly reduced primary root length relative to the control plants. GC-MS was used to determine changes in the metabolites of the primary root of maize in response to salt, drought and combined stresses. A total of 86 metabolites were measured, including 29 amino acids and amines, 21 organic acids, four fatty acids, six phosphoric acids, 10 sugars, 10 polyols, and six others. Among these, 53 metabolites with a significant change under different stresses were identified in the primary root, and the content of most metabolites showed down-accumulation. A total of four and 18 metabolites showed significant up-and down-accumulation to all three treatments, respectively. The levels of several compatible solutes, including sugars and polyols, were increased to help maintain the osmotic balance. The levels of metabolites involved in the TCA cycle, including citric acid, ketoglutaric acid, fumaric acid, and malic acid, were reduced in the primary root. The contents of metabolites in the shikimate pathway, such as quinic acid and shikimic acid, were significantly decreased. This study reveals the complex metabolic responses of the primary root to combined drought and salt stresses and extends our understanding of the mechanisms involved in root responses to abiotic tolerance in maize.

Cell Cycle Kinetic Analysis in the Cortical Regions of the Lentil Primary Root During Germination

Cell cycle kinetic activity in the cortical cells of the lentil (Lens culinaris Me-die. cv. Verte du Puy) primary root during germination was examined both temporally and spatially. Immunohistochemical and cytological evidence indicated that DNA replication and cell division started in the cortical cells of tire lentil primary root after around 13 and 17 h of imbibition, respectively. The first cells in DNA synthesis and the First mitotic figures all appeared in the cortical cells about I mm front the root-cap junction, but these divided cells had synthesized their DNA during the maturity of seed instead of during germination. The kinetic pattern of activity of the first cell cycle showed that these cells were not activated synchronously, but re-entered the cell cycle in turn depending on their places in the root tip, However, the adjacent cells partially synchronously proceeded their cell cycle.

Analysis on the Expression of TaMOR Gene in Two Different Spring Wheat Varieties at Different Years

[Objectives]The TaMOR gene is a gene that affects the initiation and growth of the secondary roots of wheat,but the expression patterns in different parts of the wheat root system and the differences in expression in different varieties are not clear.This study aimed to investigate the expression of the TaMOR gene in the seminal roots,secondary roots and root base.[Methods]Real-time fluorescence quantitative PCR technology was used to analyze the relative expression levels of the TaMOR gene in seminal roots,secondary roots and root base of seedlings of ancient variety Monkhead and modern variety Longchun 35.[Results]There was no significant difference in the number of seminal roots between Longchun 35 and Monkhead,and the numbers of seminal roots of the two varieties did not change significantly during the three sampling periods.The number of secondary roots and shoot dry weight of Longchun 35 were significantly higher than those of Monkhead,and the number of secondary roots and shoot dry weight of both varieties increased with the sampling time point.The root dry weight of Monkhead increased with the sampling time,while Longchun 35 showed the largest value at the second time.The fluorescence quantitative PCR results showed that for 13-day seedlings,the relative expression of the TaMOR gene in root base was significantly higher than that in the seminal roots and secondary roots.There was no significant difference in the relative expression of gene TaMOR in the root system of Monkhead and Longchun 35.[Conclusions]The root allocation of gramineous crops decreases with the breeding years,and the difference in gene TaMOR expression level needs further study.

The roles of microRNAs in regulating root formation and growth in plants

MicroRNAs(miRNAs) are small(ca. 20-24 nucleotides) non-coding RNAs that have recently been recognized as key post-transcriptional modulators of gene expression;and they are involved in many biological processes in plants, such as root growth and development. The miRNAs regulate root elongation, lateral root(LR) formation and adventitious root(AR) development in response to hormone signaling, nutrient uptake and biotic/abiotic stress. This review provides multiple perspectives on the involvement of miRNAs in regulating root growth and development in plants. We also discuss several crucial mechanisms of miRNAs, their relationships with transcription factors and the target gene-mediated hormone signaling interactions in the regulation of root growth and development.

The F-box protein SHORT PRIMARY ROOT modulates primary root meristem activity by targeting SEUSS-LIKE protein for degradation in rice

Root meristem activity is essential for root morphogenesis and adaptation,but the molecular mechanism regulating root meristem activity is not fully understood.Here,we identify an F-box family E3 ubiquitin ligase named SHORT PRIMARY ROOT(SHPR) that regulates primary root(PR)meristem activity and cell proliferation in rice.SHPR loss-of-function mutations impair PR elongation in rice.SHPR is involved in the formation of an SCF complex with the Oryza sativa SKP1-like protein OSK1/20.We show that SHPR interacts with Oryza sativa SEUSS-LIKE(OsSLK) in the nucleus and is required for OsSLK polyubiquitination and degradation by the ubiquitin 26S-proteasome system(UPS).Transgenic plants overexpressing OsSLK display a shorter PR phenotype,which is similar to the SHPR loss-of-function mutants.Genetic analysis suggests that SHPR promotes PR elongation in an OsSLK-dependent manner.Collectively,our study establishes SHPR as an E3 ubiquitin ligase that targets OsSLK for degradation,and uncovers a protein ubiquitination pathway as a mechanism for modulating root meristem activity in rice.

Primary root and root hair development regulation by OsAUX4 and its participation in the phosphate starvation response

Among the five members of AUX1/LAX genes coding for auxin carriers in rice,only OsAUX1 and OsAUX3 have been reported.To understand the function of the other AUX1/LAX genes,two independent alleles of osaux4 mutants,osaux4-1 and osaux4-2,were constructed using the CRISPR/Cas9 editing system.Homozygous osaux4-1 or osaux4-2 exhibited shorter primary root(PR)and longer root hair(RH)compared to the wild-type Dongjin(WT/DJ),and lost response to indoleacetic acid(IAA)treatment.OsAUX4 is intensively expressed in roots and localized on the plasma membrane,suggesting that OsAUX4 might function in the regulation of root development.The decreased meristem cell division activity and the downregulated expression of cell cycle genes in root apices of osaux4 mutants supported the hypothesis that OsAUX4 positively regulates PR elongation.OsAUX4 is expressed in RH,and osaux4 mutants showing longer RH compared to WT/DJ implies that OsAUX4 negatively regulates RH development.Furthermore,osaux4 mutants are insensitive to Pi starvation(-Pi)and OsAUX4 effects on the-Pi response is associated with altered expression levels of Pi starvation-regulated genes,and auxin distribution/contents.This study revealed that OsAUX4 not only regulates PR and RH development but also plays a regulatory role in crosstalk between auxin and-Pi signaling.

BAK1 plays contrasting roles in regulating abscisic acid-induced stomatal closure and abscisic acid-inhibited primary root growth in Arabidopsis

The mechanisms that balance plant growth and stress responses are poorly understood, but they appear to involve abscisic acid(ABA) signaling mediated by protein kinases. Here, to explore these mechanisms, we examined the responses of Arabidopsis thaliana protein kinase mutants to ABA treatment. We found that mutants of BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED RECEPTOR KINASE 1(BAK1) were hypersensitive to the effects of ABA on both seed germination and primary root growth. The kinase OPEN STOMATA 1(OST1) was more highly activated by ABA in bak1 mutant than the wild type. BAK1 was not activated by ABA treatment in the dominant negative mutant abi1-1 or the pyr1 pyl4 pyl5 pyl8 quadruple mutant, but it was more highly activated by this treatment in the abi1-2 abi2-2 hab1-1 loss-of-function triple mutant than the wild type. BAK1 phosphorylates OST1 T146 and inhibits its activity. Genetic analyses suggested that BAK1 acts at or upstream of core components in the ABA signaling pathway, including PYLs, PP2 Cs,and Sn RK2 s, during seed germination and primary root growth. Although the upstream brassinosteroid(BR) signaling components BAK1 and BR INSENSITIVE 1(BRI1) positively regulate ABAinduced stomatal closure, mutations affecting downstream components of BR signaling, including BRASSINOSTEROID-SIGNALING KINASEs(BSKs)and BRASSINOSTEROID-INSENSITIVE 2(BIN2), did not affect ABA-mediated stomatal movement. Thus,our study uncovered an important role of BAK1 in negatively regulating ABA signaling during seed germination and primary root growth, but positively modulating ABA-induced stomatal closure, thus optimizing the plant growth under drought stress.

HY5 regulates light-responsive transcription of microRNA163 to promote primary root elongation in Arabidopsis seedlings

MicroRNAs(miRNAs)play key roles in the post-transcriptional regulation of gene expression in plants.Many miRNAs are responsive to environmental signals.Light is the first environmental signal perceived by plants after emergence from the soil.However,less is known about the roles and regulatory mechanism of miRNAs in response to light signal.Here,using small RNA sequencing,we determined that miR163 is significantly rapidly induced by light signaling in Arabidopsis thaliana seedlings.The light-inducible response of miR163 functions genetically downstream of LONG HYPOCOTYL 5(HY5),a central positive regulator of photomorphogenesis.HY5 directly binds to the two G/C-hybrid elements in the miR163 promoter with unequal affinity;one of these elements,which is located next to the transcription start site,plays a major role in light-induced expression of miR163.Overexpression of miR163 rescued the defective primary root elongation of hy5 seedlings without affecting lateral root growth,whereas overexpressing of miR163 target PXMT1 inhibited primary root elongation.These findings provide insight into understanding the post-transcriptional regulation of root photomorphogenesis mediated by the HY5-miR163-PXMT1 network.

OsRLR4 binds to the OsAUX1 promoter to negatively regulate primary root development in rice

Root architecture is one of the most important agronomic traits that determines rice crop yield. The primary root(PR) absorbs mineral nutrients and provides mechanical support;however, the molecular mechanisms of PR elongation remain unclear in rice. Here, the two loss-of-function T-DNA insertion mutants of root length regulator 4(Os RLR4), osrlr4-1 and osrlr4-2 with longer PR, and three Os RLR4 overexpression lines, OE-Os RLR4-1/-2/-3 with shorter PR compared to the wild type/Hwayoung(WT/HY), were identified. Os RLR4 isone of five members of the PRAF subfamily of the regulator chromosome condensation1(RCC1) family. Phylogenetic analysis of Os RLR4 from wild and cultivated rice indicated that it is under selective sweeps, suggesting its potential role in domestication. Os RLR4 controls PR development by regulating auxin accumulation in the PR tip and thus the root apical meristem activity. A series of biochemical and genetic analyses demonstrated that Os RLR4 functions directly upstream of the auxin transporter Os AUX1. Moreover, Os RLR4 interacts with the TRITHORAX-like protein Os Trx1 to promote H3 K4 me3 deposition at the Os AUX1 promoter, thus altering its transcription level. This work provides insight into the cooperation of auxin and epigenetic modifications in regulating root architecture and provides a genetic resource for plant architecture breeding.

Initial exploration of the mechanism underlying H2O2-induced root horizontal bending in pea

It was reported that exogenous hydrogen peroxide （H2O2） can induce primary root bend in Arabidopsis and pea. However, the mechanism remains unclear. Here we explored the mechanism underlying this phenomenon by using the pea （Pisum sativum L.） variety ＂longwan No. 1＂ The results showed that the endogenous indole-3-acetic acid （IAA） content decreased and gibberellin A3 （GA3） content increased in the curving primary pea root induced by H2O2. Meanwhile, both of the two hormones asymmetrically distributed in the inside and outside parts of the curving root. Also, the starch content decreased due to the increased a-amylase activity in this process. However, exogenous Ca2＋ can relieve the horizontal bending of pea root induced by H2O2 and altered the contents of endogenous IAA and GA3. A working model was proposed： Exogenous H2O2 causes the increase in GA3 content, and GA3 stimulates the activity of or-amylase, which leads to the hydrolysis of starch, and then the root lost the gravity perceiving. The asymmetric distribution of IAA and GA3 in two sides of curving root may cause the horizontal bending.Exogenous Ca^2＋ can relieve root bending through altering the endogenous IAA and GA3 contents.