Effects of Aluminium Toxicity on Root and Shoot Growth Of Rice and Chickpea Seedlings

Increasing concentrations of aluminium progressively declined primary root length and number of lateral roots in rice and chickpea seedlings grown in rhizobox. It also inhibited the root and shoot length, dry weight of root and shoot of rice and chickpea seedlings grown in solution culture. On the other hand, it enhanced shoot/root length ratio and dry weight ratio for both the genera. Bangladesh J. Bot. 50(4): 1195-1201, 2021 (December)

The Overexpression of NUC Promotes Development and Increases Resistance to Nitrogen Deficiency in Arabidopsis thaliana

NUTCRACKER (NUC) is a transcription factor expressed in multiple tissues, but little is known about its physiological roles. In this study, we explored the physiological function of NUC with the Arabidopsis knockout, rescue, and overexpression lines. We found that NUC overexpression promoted development at the germination, seedling, and juvenile stages. NUC overexpression increased resistance to nitrogen (N) deficiency stress by increasing the chlorophyll content, suppressing anthocyanin accumulation, and increasing the biomass under N deficiency. In contrast, the absence of NUC did not affect such characteristics. N deficiency significantly increased the expression of NUC in leaves but did not affect the expression of NUC in roots. The overexpression of NUC promoted primary root length under both normal and N deficiency conditions. Furthermore, we found that the N-responsive and lateral-root-related genes TGA1 and NRT2.4 had NUC-binding sites in their promoter regions and that their expression was upregulated by NUC under N deficiency. The overexpression of the NUC increased the number and length of the lateral roots under N deficiency through inducible promotion. Multiple lines of investigation suggest that the regulatory function of the NUC could be bypassed through its redundant MAGPIE (MGP) when the NUC is absent. Our findings provide novel insight into NUC’s functions and will assist efforts to improve plants’ development and resistance to nutrient stresses.

Non-TZF Protein AtC3H59/ZFWD3 Is Involved in Seed Germination, Seedling Development, and Seed Development, Interacting with PPPDE Family Protein Desi1 in Arabidopsis

Despite increasing reports on the function of CCCH zinc finger proteins in plant development and stress response, the functions and molecular aspects of many non-tandem CCCH zinc finger (non-TZF) proteins remain uncharacterized. AtC3H59/ZFWD3 is an Arabidopsis non-TZF protein and belongs to the ZFWD subfamily harboring a CCCH zinc finger motif and a WD40 domain. In this study, we characterized the biological and molecular functions of AtC3H59, which is subcellularly localized in the nucleus. The seeds of AtC3H59-overexpressing transgenic plants (OXs) germinated faster than those of wild type (WT), whereas atc3h59 mutant seeds germinated slower than WT seeds. AtC3H59 OX seedlings were larger and heavier than WT seedlings, whereas atc3h59 mutant seedlings were smaller and lighter than WT seedlings. Moreover, AtC3H59 OX seedlings had longer primary root length than WT seedlings, whereas atc3h59 mutant seedlings had shorter primary root length than WT seedlings, owing to altered cell division activity in the root meristem. During seed development, AtC3H59 OXs formed larger and heavier seeds than WT. Using yeast two-hybrid screening, we isolated Desi1, a PPPDE family protein, as an interacting partner of AtC3H59. AtC3H59 and Desi1 interacted via their WD40 domain and C-terminal region, respectively, in the nucleus. Taken together, our results indicate that AtC3H59 has pleiotropic effects on seed germination, seedling development, and seed development, and interacts with Desi1 in the nucleus via its entire WD40 domain. To our knowledge, this is the first report to describe the biological functions of the ZFWD protein and Desi1 in Arabidopsis.

Glucose-6-Phosphate Dehydrogenase Is Involved in the Tolerance of Soybean Seedlings to Low Nitrogen Stress

Nitrogen (N) deficiency affects plant growth and crop yield. In this study, we investigated the role of glucose-6-phosphate dehydrogenase (G6PDH) in response to N availability in three soybean cultivars, JINDOU 19 (JD19), LONGHUANG 3 (LH3), and LONGDOU 2 (LD2), that have different tolerances to low-N stress. The results showed that the leaf area and primary root length of JD19 and LH3 were greater than that of LD2 under low-N stress, suggesting that the growth of JD19 and LH3 were impaired less than LD2, and thus are more tolerant to low-N stress than LD2 is. Interestingly, the G6PDH expression showed different degrees of change in these soybean cultivars under low-N conditions, and the G6PDH activity in JD19 and LH3 was higher than that in LD2. When G6PDH was inhibited by glucosamine (GlcN), the contents of malondialdehyde (MDA) and H2O2 were dramatically increased under low-N stress. Meanwhile, the activities of N metabolism-related enzymes were inhibited. These results indicate that G6PDH is involved in the tolerance of soybean cultivars to low-N stress through affecting the N metabolism. Furthermore, under low-N conditions, the contents of NADP+ and reduced glutathione (GSH) in JD19 and LH3 were increased more than that in LD2. In contrast, the activity of the plasma membrane (PM), NADPH oxidase, and the NADPH content in JD19 and LH3 were lower than that in LD2. In conclusion, G6PDH reduces the accumulation of ROS in plant cells by modulating NADPH/NADP+ and GSH levels to maintain the growth of soybeans under low-N conditions.

Solanum lycopersicum Seedlings. Metabolic Responses Induced by the Alkamide Affinin

Alkamides have been observed to interact in different ways in several superior organisms and have been used in traditional medicine in many countries e.g., to relieve pain. Previous studies showed that affinin when applied to other plant species induces prominent changes in the root architecture and induces transcriptional adjustments; however, little is known about the metabolic pathways recruited by plants in response to alkamides. Previous published work with Arabidopsis seedlings treated in vitro with affinin at 50 µM significantly reduced primary root length. In tomato seedlings, that concentration did not reduce root growth but increase the number and length of lateral roots. Non-targeted metabolomic analysis by Gas Chromatography couplet to Mass Spectrometry (GC/EIMS) showed that, in tomato seedlings, affinin increased the accumulation of several metabolites leading to an enrichment of several metabolic pathways. Affinin at 100 µM alters the accumulation of metabolites such as organic acids, amino acids, sugars, and fatty acids. Finally, our results showed a response possibly associated with nitrogen, GABA shunt and serine pathways, in addition to a possible alteration in the mitochondrial electron transport chain (ETC), interesting topics to understand the molecular and metabolic mechanisms in response to alkamide in plants.

Mapping and validation of a major QTL for primary root length of soybean seedlings grown in hydroponic conditions

Background The root system provides nutrient absorption and is closely related to abiotic stress tolerance, but it is difficult to study the roots under field conditions. This study was conducted to identify quantitative trait loci (QTL) associated with primary root length (PRL) during soybean seedling growth in hydroponic conditions. A total of 103 F7 recombinant inbred lines (RILs) derived from a cross between K099 (short primary root) and Fendou 16 (long primary root) were used to identify QTL for PRL in soybean. The RIL population was genotyped with 223 simple sequence repeats markers covering 20 chromosomes. Phenotyping for primary root length was performed for 3-weeks plants grown in hydoponic conditions. The identified QTL was validated in near isogenic lines and in a separate RIL population. Results QTL analysis using inclusive composite interval mapping method identified a major QTL on Gm16 between SSR markers Sat_165 and Satt621, explaining 30.25 % of the total phenotypic variation. The identified QTL, qRL16.1, was further confirmed in a segregating population derived from a residual heterozygous line (RHLs-98). To validate qRL16.1 in a different genetic background, QTL analysis was performed in another F6 RIL population derived from a cross between Union (medium primary root) and Fendou 16, in which a major QTL was detected again in the same genomic region as qRL16.1, explaining 14 % of the total phenotypic variation for PRL. In addition, the effect of qRL16.1 was confirmed using two pair of near-isogenic lines (NILs). PRL was significantly higher in NILs possessing the qRL16.1 allele from Fendou 16 compared to allele from K099. Conclusions The qRL16.1 is a novel QTL for primary root length in soybean which provides important information on the genetic control of root development. Identification of this major QTL will facilitate positional cloning and DNA marker-assisted selection for root traits in soybean.

Drought Stress Induces Differential DNA Methylation Shift at Symmetric and Asymmetric Cytosine Sites in the Promoter Region of ZmEXPB2 Gene in Maize

β-expansin 2 (EXPB2) gene induces drought tolerance in different plant species including maize. Different epigenetic mechanisms like DNA methylation, histone modification and RNA interference affect the gene activities under stress conditions. DNA methylation, an important epigenetic mechanism, could be involved in the regulation of ZmEXPB2 gene under drought stress in maize. Plants of drought sensitive variety „Jalal‟ were grown till 4th leaf stage under well-watered conditions. At 5th leaf stage, plants were divided in two groups i.e., well-watered (100% water holding capacity) or drought stress (0% water holding capacity for 15 days). Plants subjected to drought stress showed clear signs of stress by significant decrease in fresh weight of whole plant, 6th leaf length, stunted secondary root growth and increased primary root length. DNA methylation profile of three regions (denoted as -1.7 k, -1.3 k and -0.8 k) in the promoter of ZmEXPB2 gene, of root DNA, were evaluated. Under well-watered conditions, heterogeneity in DNA methylation profile along the promoter sequence was observed. Regions -1.7 k and -1.3 k were methylated whereas the region -0.8 k was nonmethylated. After the comparison of DNA methylation profile of well-watered and drought stress plants, no change in -1.7 k and -0.8 k regions was observed. However, the -1.3k region had significant decrease in the DNA methylation at symmetric cytosine sites i.e., cytosine-guanine (CG) dinucleotides and cytosine-adenine/cytosine/thymine-guanine (CHG where H = A, C or T) trinucleotide and significant increase at asymmetric cytosine sites (CHH) under the stress condition. In addition, significant increase in the gene expression of ZmEXPB2 under drought was also observed. In conclusion, drought stress conditions induce DNA hypomethylation at CG, and CHG sites and DNA hypermethylation at CHH sites in the middle region of the promoter of ZmEXPB2 gene. This shift can be associated with the up regulation of ZmEXPB2 gene which in turn increased primary root length as a plant stress response mechanism. © 2021 Friends Science Publishers

Genotypic variability of root and shoot traits of bread wheat (Triticum aestivum L.) at seedling stage

The evaluation of the embryonic root and stem of bread wheat (Triticum aestivum L.) in the early stage of development (seedling stage) can be a powerful tool in wheat breeding aimed at obtaining progenies with a greater early vigour. It is revealed that genotypes with faster early vigour have produced higher biomass and grain yield. In this study, the evaluation of traits of the embryonic root and the embryonic stem of 101 bread wheat genotypes was preformed at the 10-day old seedlings. The following eight morphological traits of roots and stems were analysed: primary root length, branching interval, the number of roots, total length of lateral roots, angle of seminal roots, stem length, root dry weight and the stem dry weight. Analysed lateral roots included seminal roots. The greatest, i.e. the smallest variability of observed traits was detected in the branching interval, i.e. the stem length, respectively. The highest positive correlation was determined between the primary root length and the total length of lateral roots. The cluster analysis, based on observed traits, shows that genotypes were clearly divided into two main clusters, A and B. The two clusters essentially differed from each other in the values of the following traits: primary root length, total length of lateral roots, root dry weight, stem dry weight and the stem length. Genotypes with shorter primary and lateral roots, lower root and stem dry weight and a shorter stem were grouped in the cluster B. On the other hand, the cluster A encompassed genotypes with values of these traits above or around the average. The values of the remaining analysed traits: the angle of seminal roots, the number of lateral roots and the branching interval varied greatly between obtained clusters. The cluster analysis showed the homogeneity of genotypes originating from Serbia and the region; their values of the root and stem length and weight were mostly around and below the average. However, the values of the angle of seminal roots, number of lateral roots and the branching interval were above average.

Effects of Phosphate Shortage on Root Growth and Hormone Content of Barley Depend on Capacity of the Roots to Accumulate ABA

Although changes in root architecture in response to the environment can optimize mineral and water nutrient uptake, mechanisms regulating these changes are not well-understood. We investigated whether P deprivation effects on root development are mediated by abscisic acid (ABA) and its interactions with other hormones. The ABA-deficient barley mutant Az34 and its wild-type (WT) were grown in P-deprived and P-replete conditions, and hormones were measured in whole roots and root tips. Although P deprivation decreased growth in shoot mass similarly in both genotypes, only the WT increased primary root length and number of lateral roots. The effect was accompanied by ABA accumulation in root tips, a response not seen in Az34. Increased ABA in P-deprived WT was accompanied by decreased concentrations of cytokinin, an inhibitor of root extension. Furthermore, P-deficiency in the WT increased auxin concentration in whole root systems in association with increased root branching. In the ABA-deficient mutant, P-starvation failed to stimulate root elongation or promote branching, and there was no decline in cytokinin and no increase in auxin. The results demonstrate ABA’s ability to mediate in root growth responses to P starvation in barley, an effect linked to its effects on cytokinin and auxin concentrations.

A genome-wide association study reveals that the glucosyltransferase OsIAGLU regulates root growth in rice

Good root growth in the early post-germination stages is an important trait for direct seeding in rice, but its genetic control is poorly understood. In this study, we examined the genetic architecture of variation in primary root length using a diverse panel of 178 accessions. Four QTLs for root length (qRL3, qRL6, qRL7, and qRL11) were identified using genome-wide association studies. One candidate gene was validated for the major QTL qRL11, namely the glucosyltransferase OsIAGLU. Disruption of this gene in Osiaglu mutants reduced the primary root length and the numbers of lateral and crown roots. The natural allelic variations of OsIAGLU contributing to root growth were identified. Functional analysis revealed that OsIAGLU regulates root growth mainly via modulating multiple hormones in the roots, including levels of auxin, jasmonic acid, abscisic acid, and cytokinin. OsIAGLU also influences the expression of multiple hormone-related genes associated with root growth. The regulation of root growth through multiple hormone pathways by OsIAGLU makes it a potential target for future rice breeding for crop improvement.