Plant height plays an important role in the potential and stability of crop yields and represents one of the most important agronomic traits of wheat. Although more than 30 dwarfing genes have been identified in wheat, only a few are used in wheat breeding, which has narrowed the genetic basis of newly developed varieties. Therefore, continually identifying new dwarfing genes is required to produce improved wheat cultivars. TA001 is a new germplasm line marked by reduced plant height and early maturation, and it was derived from a hybridization between the common wheat Yannong 15 and the Aegilops ventricosa × Aegilops cylindrica amphiploid SDAU18. In this study, cytological observations, agronomic trait examinations, genomic in situ hybridization (GISH), multicolor genomic in situ hybridization (mc-GISH), multicolor fluorescence in situ hybridization (mc-FISH), SSR analysis and seed storage protein electrophoresis were combined to determine the cytological stability, main agronomic traits, chromosomal constituents and seed storage protein subunits of TA001. Twenty-one bivalents were observed in most of the pollen mother cells at metaphase I (PMCs MI) in TA001, which housed 42 chromosomes, and the chromosomes in most pollen mother cells at anaphase I (PMCs AI) displayed 21/21 segregation. Twenty bivalents plus two univalents were simultaneously observed in most of the PMCs MI of the hybrid F1 between TA001 and Yannong 15. TA001 possessed all chromosomes from genomes A, B and D except for chromosome 7B, which was replaced by one pair of N-genome chromosomes from Aegilops ventricosa. Several pairs of chromosomes in TA001 exhibited different FISH patterns from the equivalent chromosomes in Yannong 15. TA001 housed alien genetic materials from Aegilops ventricosa and Aegilops cylindrica and possessed new glutenin and gliadin subunits specific to SDAU18, as revealed by molecular marker analysis and protein electrophoresis respectively.
The root appears to be the most relevant organ for breeding drought stress tolerance. However, our knowledge about temporal and spatial regulation of drought-associated genes in the root remains fragmented, especially in crop plants. We performed a meta-analysis of expression divergence of essential drought-inducible genes and analyzed their association with cis-elements in model crops and major cereal crops. Our analysis of 42 selected drought-inducible genes revealed that these are expressed primarily in roots, followed by shoot, leaf, and inflorescence tissues, especially in wheat. Quantitative real-time RT-PCR analysis confirmed higher expression of TaDREB2 and TaAQP7 in roots, correlated with extensive rooting and drought-stress tolerance in wheat. A promoter scan up to 2 kb upstream of the translation start site using phylogenetic footprinting revealed 708 transcription factor binding sites, including drought response elements (DREs), auxin response elements (AuxREs), MYCREs/MYBREs, ABAREs, and ERD1 in 19 selected genes. Interestingly, these elements were organized into clusters of overlapping transcription factor binding sites known as homotypic clusters (HCTs), which modulate drought physiology in plants. Taken together, these results revealed the expression preeminence of major drought-inducible genes in the root, suggesting its crucial role in drought adaptation. The occurrence of HCTs in drought-inducible genes highlights the putative evolutionary modifications of crop plants in developing drought adaptation. We propose that these DNA motifs can be used as molecular markers for breeding drought-resilient cultivars, particularly in the cereal crops.
The engineering of plants with enhanced tolerance to abiotic stresses typically involves complex multigene networks and may therefore have a greater potential to introduce unintended effects than the genetic modification for simple monogenic traits. For this reason, it is essential to study the unintended effects in transgenic plants engineered for stress tolerance. We selected drought- and salt-tolerant transgenic wheat overexpressing the transcription factor, GmDREB1, to investigate unintended pleiotropic effects using RNA-seq analysis. We compared the transcriptome alteration of transgenic plants with that of wild-type plants subjected to salt stress as a control. We found that GmDREB1 overexpression had a minimal impact on gene expression under normal conditions. GmDREB1 overexpression resulted in transcriptional reprogramming of the salt response, but many of the genes with differential expression are known to mitigate salt stress and contribute incrementally to the enhanced stress tolerance of transgenic wheat. GmDREB1 overexpression did not activate unintended gene networks with respect to gene expression in the roots of transgenic wheat. This work is important for establishing a method of detecting unintended effects of genetic engineering and the safety of such traits with the development of marketable transgenic crops in the near future.
Salinity-imposed limitations on plant growth are manifested through osmotic and ionic imbalances. However, because salinity-induced responses vary considerably among crop plants, monitoring of such responses at an early stage has relevance. In this study, physiological (seed germination, seed vigor index, root length, shoot length, fresh weight, dry weight) and biochemical attributes (osmoprotectants, K+/Na+ ratio) were analyzed for a time-course assessment of salt responses in Indian mustard (Brassica juncea L.) with an emphasis on early monitoring. The results showed strong correlations for total soluble sugars at germination phase (24 h), proline content in the seedling establishment phase (48 h) and various physiological parameters including seed vigor index (R2 = 0.901), shoot length (R2 = 0.982), and fresh weight (R2 = 0.980) at 72 h (adaptation under stress). In addition, transcriptional changes were observed under NaCl treatment for key genes belonging to the family of selective ion transporters (NHX, HKT) and abscisic acid synthesis (AAO-3). The status of mitochondrial respiration was also examined as a probe for salinity tolerance at an early stage. The results suggested that although all the analyzed parameters showed correlations (negative or positive) with salt stress magnitude, their critical response times differed, with most of the studied biochemical, physiological, or molecular markers providing valuable information only after radicle emergence, whereas mitochondrial respiration via alternative oxidase was useful for the early detection of salt responses.
In wheat, the ear is one of the main photosynthetic contributors to grain filling under drought stress conditions. In order to determine the relationship between stomatal characteristics and plant drought resistance, photosynthetic and stomatal characteristics and water use efficiency (WUE) were studied in two wheat cultivars: the drought-resistant cultivar ‘Changhan 58’ and the drought-sensitive cultivar ‘Xinong 9871’. Plants of both cultivars were grown in pot conditions under well-watered (WW) and water-stressed (WS) conditions. In both water regimes, ‘Changhan 58’ showed a significantly higher ear photosynthetic rate with a lower rate of variation and a significantly higher percentage variation of transpiration compared to control plants at the heading stage under WS conditions than did ‘Xinong 9871’ plants. Moreover, ‘Changhan 58’ showed lower stomatal density (SD) and higher stomatal area per unit organ area (A) under both water conditions. Water stress decreased SD, A, and stomatal width (SW), and increased stomatal length in flag leaves (upper and lower surfaces) and ear organs (awn, glume, lemma, and palea), with the changes more pronounced in ear organs than in flag leaves. Instantaneous WUE increased slightly, while integral WUE improved significantly in both cultivars. Integral WUE was higher in ‘Changhan 58’, and increased by a greater amount, than in ‘Xinong 9871’. These results suggest that drought resistance in ‘Changhan 58’ is regulated by stomatal characteristics through a decrease in transpiration rate in order to improve integral WUE and photosynthetic performance, and through sustaining a higher ear photosynthetic rate, therefore enhancing overall drought-resistance.
This study investigated the effect of salicylic acid (SA) and sodium nitroprusside (SNP; NO donor) on nickel (Ni) toxicity in germinating finger millet seedlings. Fourteen-day-old finger millet plants were subjected to 0.5 mmol L− 1 Ni overload and treated with 0.2 mmol L− 1 salicylic acid and 0.2 mmol L− 1 sodium nitroprusside to lessen the toxic effect of Ni. The Ni overload led to high accumulation in the roots of growing plants compared to shoots, causing oxidative stress. It further reduced root and shoot length, dry mass, total chlorophyll, and mineral content. Exogenous addition of either 0.2 mmol L− 1 SA or 0.2 mmol L− 1 SNP reduced the toxic effect of Ni, and supplementation with both SA and SNP significantly reduced the toxic effect of Ni and increased root and shoot length, chlorophyll content, dry mass, and mineral concentration in Ni-treated plants. The results show that oxidative stress can be triggered in finger millet plants by Ni stress by induction of lipoxygenase activity, increase in levels of proline, O2•− radical, MDA, and H2O2, and reduction in the activity of antioxidant enzymes such as CAT, SOD, and APX in shoots and roots. Exogenous application of SA or SNP, specifically the combination of SA + SNP, protects finger millet plants from oxidative stress observed under Ni treatment.
Drought stress is one of the most severe environmental constraints to plant growth and crop productivity. Plant growth is greatly affected by drought stress, and plants, to survive, adapt to this stress by invoking different pathways. Piriformospora indica, a root-colonizing endophytic fungus of Sebacinales, promotes plant growth and confers resistance to biotic and abiotic stresses, including drought stress, by affecting the physiological properties of the host plant. The fungus strongly colonizes the roots of maize (Zea mays L.) and promotes shoot and root growth under both normal growth conditions and drought stress. We used polyethylene glycol (PEG-6000) to mimic drought stress and found that root fresh and dry weight, leaf area, SPAD value, and leaf number were increased in P. indica-colonized plants. The antioxidative activities of catalases and superoxide dismutases were upregulated within 24 h in the leaves of P. indica-colonized plants. Drought-related genes DREB2A, CBL1, ANAC072, and RD29A were upregulated in drought-stressed leaves of P. indica-colonized plants. Furthermore, after drought treatment, proline content increased, whereas accumulation of malondialdehyde (MDA), an indicator of membrane damage, decreased in P. indica-colonized maize. We conclude that P. indica-mediated plant protection against the detrimental effects of drought may result from enhanced antioxidant enzyme activity, proline accumulation, and expression of drought-related genes and lower membrane damage in maize plants.
Two important mycotoxins, aflatoxin and fumonisin, are among the most potent naturally occurring carcinogens, contaminating maize (Zea mays) and affecting crop yield and quality. Resistance of maize to pre-harvest mycotoxin contamination, specifically aflatoxin produced by Aspergillus flavus and fumonisin produced by Fusarium verticillioides, is a goal in breeding programs that screen for these important traits with the aim of developing resistant commercial hybrids. We conducted two years of field evaluations on 87 inbred lines originating primarily in China and Mexico and not previously screened for resistance. The objectives of our study were to identify resistant germplasm for breeding purposes and to examine possible relationships between resistances to the two mycotoxins. Aflatoxin and fumonisin were present in samples harvested from all lines in both years. Concentrations of total aflatoxin ranged from 52.00 ± 20.00 to 1524.00 ± 396.00 μg kg− 1, while those of fumonisin ranged from 0.60 ± 0.06 to 124.00 ± 19.50 mg kg− 1. The inbred lines TUN15, TUN61, TUN37, CY2, and TUN49 showed the lowest aflatoxin accumulation and CN1, GT601, TUN09, TUN61, and MP717 the lowest fumonisin accumulation. TUN61 showed the lowest accumulation of both mycotoxins. This study confirmed previous observations that high levels of aflatoxin can coexist with fumonisin, with 55 maize lines showing a positive correlation coefficient between the concentrations of aflatoxin and fumonisin and 32 lines showing a negative correlation coefficient. These selected lines, particularly TUN61, may provide sources of resistance to mycotoxin contamination in breeding programs. However, the mechanism of resistance in this germplasm remains to be identified. Future research should also address factors that influence the fungus-plant interaction, such as herbivory and environmental stress.
Fertilizer plays an important role in increasing rice yield. More than half of all fertilizer applied to the field is not taken up, resulting in environmental damage and substantial economic losses. To address these concerns, a low-cost, coated compound fertilizer named “Xiang Nong Da” (XND), requiring only a single basal application, was studied. A two-year field experiment was conducted to test the effects of XND application on rice yield and nitrogen fertilizer use efficiency. An ordinary uncoated compound fertilizer (UNCF), with 20% more nutrients and split application was selected as the control. The yield of XND-treated rice was only 3.1% lower than that of the control, an insignificant difference. There were no significant differences between N use efficiency indices of the two fertilizer treatments except for N partial factor productivity (PFPN). PFPN of XND treatment was 19.7%-23.2% higher than the control, a significant difference. This result indicates that a 20% decrease in N application rate is possible with XND without yield reduction and with savings in both labor and time.
