Optimizing plant spatial competition can change phytohormone content and promote tillering, thereby improving wheat yield.

As an important type of interplant competition, line-spacing shrinkage and row-spacing expansion (LSRE) can increase the number of tillers and improve resource utilization efficiency in wheat. Wheat tillering is closely related to various phytohormones. However, it is unclear whether LSRE regulates phytohormones and their relationship to tillering and wheat yield. This study evaluated tillering characteristics, phytohormone content in tiller nodes at the pre-winter stage, and grain yield factors for the winter wheat variety Malan1. We used a two-factor randomized block trial design with two sowing spacings of 15 cm (15RS, conventional treatment) and 7.5 cm (7.5RS, LSRE treatment) at the same density and three sowing-date groups (SD1, SD2, and SD3). LSRE significantly promoted wheat tillering and biomass at the pre-winter stage (average increases of 14.5% and 20.9% in the three sowing-date groups, respectively) and shortened the accumulated temperature required for a single tiller. Changes in the levels of phytohormones, including decreased gibberellin and indole acetic acid and increased zeatin riboside and strigolactones, were determined by high-performance liquid chromatography and were shown to be responsible for the tillering process under LSRE treatment in winter wheat. LSRE treatment can improve crop yield by increasing the number of spikes per unit area and grain weight. Our results clarified the changes in tillering and phytohormones content of winter wheat under LSRE treatment and their correlation with grain yield. This study also provides insights into the physiological mechanisms of alleviating inter-plant competition to improve crop yield.

GmTDN1 improves wheat yields by inducing dual tolerance to both drought and low-N stress.

Genetically enhancing drought tolerance and nutrient use efficacy enables sustainable and stable wheat production in drought-prone areas exposed to water shortages and low soil fertility, due to global warming and declining natural resources. In this study, wheat plants, exhibiting improved drought tolerance and N-use efficacy, were developed by introducing GmTDN1, a gene encoding a DREB-like transcription factor, into two modern winter wheat varieties, cv Shi4185 and Jimai22. Overexpressing GmTDN1 in wheat resulted in significantly improved drought and low-N tolerance under drought and N-deficient conditions in the greenhouse. Field trials conducted at three different locations over a period of 2-3 consecutive years showed that both Shi4185 and Jimai22 GmTDN1 transgenic lines were agronomically superior to wild-type plants, and produced significantly higher yields under both drought and N-deficient conditions. No yield penalties were observed in these transgenic lines under normal well irrigation conditions. Overexpressing GmTDN1 enhanced photosynthetic and osmotic adjustment capacity, antioxidant metabolism, and root mass of wheat plants, compared to those of wild-type plants, by orchestrating the expression of a set of drought stress-related genes as well as the nitrate transporter, NRT2.5. Furthermore, transgenic wheat with overexpressed NRT2.5 can improve drought tolerance and nitrogen (N) absorption, suggesting that improving N absorption in GmTDN1 transgenic wheat may contribute to drought tolerance. These findings may lead to the development of new methodologies with the capacity to simultaneously improve drought tolerance and N-use efficacy in cereal crops to ensure sustainable agriculture and global food security.

Overexpression of soybean DREB1 enhances drought stress tolerance of transgenic wheat in the field.

Drought-response-element binding (DREB)-like transcription factors can significantly enhance plant tolerance to water stress. However, most research on DREB-like proteins to date has been conducted in growth chambers or greenhouses, so there is very little evidence available to support their practical use in the field. In this study, we overexpressed GmDREB1 from soybean in two popular wheat varieties and conducted drought-tolerance experiments across a range of years, sites, and drought-stress regimes. We found that the transgenic plants consistently exhibited significant improvements in yield performance and a variety of physiological traits compared with wild-type plants when grown under limited water conditions in the field, for example showing grain yield increases between 4.79-18.43%. Specifically, we found that the transgenic plants had reduced membrane damage and enhanced osmotic adjustment and photosynthetic efficiency compared to the non-transgenic controls. Three enzymes from the biosynthetic pathway of the phytohormone melatonin were up-regulated in the transgenic plants, and external application of melatonin was found to improve drought tolerance. Together, our results demonstrate the utility of transgenic overexpression of GmDREB1 to improve the drought tolerance of wheat in the field.

Improved drought tolerance in wheat plants overexpressing a synthetic bacterial cold shock protein gene SeCspA.

Cold shock proteins (CSPs) enhance acclimatization of bacteria to adverse environmental circumstances. The Escherichia coli CSP genes CspA and CspB were modified to plant-preferred codon sequences and named as SeCspA and SeCspB. Overexpression of exogenous SeCspA and SeCspB in transgenic Arabidopsis lines increased germination rates, survival rates, and increased primary root length compared to control plants under drought and salt stress. Investigation of several stress-related parameters in SeCspA and SeCspB transgenic wheat lines indicated that these lines possessed stress tolerance characteristics, including lower malondialdehyde (MDA) content, lower water loss rates, lower relative Na+ content, and higher chlorophyll content and proline content than the control wheat plants under drought and salt stresses. RNA-seq and qRT-PCR expression analysis showed that overexpression of SeCsp could enhance the expression of stress-responsive genes. The field experiments showed that the SeCspA transgenic wheat lines had great increases in the 1000-grain weight and grain yield compared to the control genotype under drought stress conditions. Significant differences in the stress indices revealed that the SeCspA transgenic wheat lines possessed significant and stable improvements in drought tolerance over the control plants. No such improvement was observed for the SeCspB transgenic lines under field conditions. Our results indicated that SeCspA conferred drought tolerance and improved physiological traits in wheat plants.

A R2R3-MYB transcription factor gene in common wheat (namely TaMYBsm1) involved in enhancement of drought tolerance in transgenic Arabidopsis.

We isolated the TaMYBsm1 genes, encoding R2R3-type MYB proteins in common wheat, aimed to uncover the possible molecular mechanisms related to drought response. The TaMYBsm1 genes, TaMYBsm1-A, TaMYBsm1-B and TaMYBsm1-D, were isolated and analyzed from the common wheat cultivar Shimai 15. Their expression patterns under PEG 6000 and mannitol were monitored by semi-quantitative RT-PCR and ß-glucuronidase (Gus) assay. The function of TaMYBsm1-D under drought stress in transgenic Arabidopsis plants was investigated, and the germination rate, water loss rate, as well as the proline and malondialdehyde (MDA) content were compared with that in wild type (WT) plants. The expression of three downstream genes (DREB2A, P5CS1 and RD29A) in TaMYBsm1-D transgenic plants was analyzed. The R2R3-MYB domains of the MYBsm1 proteins were highly conserved in plants. In addition, the TaMYBsm1 proteins were targeted to the nucleus and contained transcriptional activation domains (TADs). Gus assay and semi-quantitative RT-PCR analysis demonstrated that the TaMYBsm1 genes were up-regulated when the wheat was treated by PEG and mannitol. Compared with WT plants, the germination rates were much higher, but the water loss rates were much lower in TaMYBsm1-D overexpression plants. TaMYBsm1-D transgenic plants showed distinct higher proline contents but a lower MDA content than the WT plants. The three downstream genes were highly expressed in TaMYBsm1-D transgenic plants. We concluded from these results that TaMYBsm1 genes play an important role in plant drought stress tolerance through up-regulation of DREB2A, P5CS1 and RD29A. The increase of proline content and decrease of MDA content may also be involved in the drought response.

A major locus controlling malondialdehyde content under water stress is associated with Fusarium crown rot resistance in wheat.

Malondialdehyde (MDA) is a naturally occurring product of lipid peroxidation and the level of MDA in plant is often used as a parameter to evaluate the damage to plants' cells due to stress. Plant with lower amounts of MDA under drought conditions is generally considered as more tolerant to drought. In this study, a population of recombinant inbred lines was used to map the quantitative trait locus (QTLs) that controlled MDA content under well-watered condition (WW) and water deficit (WD) condition. A major QTL, designated as Qheb.mda-3B, was detected on the long arm of chromosome 3B. Based on interval mapping analysis, Qheb.mda-3B explained 31.5 and 39.0 % of the phenotypic variance under WW and WD conditions, respectively. Qheb.mda-3B was located in the same interval as a previously identified QTL (Qcrs.cpi-3B) that controlled resistance to Fusarium crown rot (FCR), a fungal disease caused by Fusarium species. Three pairs of near-isogenic lines (NILs) previously developed for Qcrs.cpi-3B were found to show significant differences in MDA content under WD condition. These results suggested that same set of genes is likely to be involved in drought tolerance and FCR resistance in wheat.

Distribution of genes associated with yield potential and water-saving in Chinese Zone II wheat detected by developed functional markers.

Functional markers (FMs) developed from sequence polymorphisms are present in allelic variants of a functional gene at a locus and are directly associated with phenotypic variations. In this study, FM linked to Rht-B1, Rht-D1, TaCwi-A1, TaSus2-2B, TaGW2-6A and Dreb-B1 genes conferring to yield potential and water-saving were selected to analyse the distribution in 102 wheat varieties, most of which were authorized in the past decade and adapted to grow in Zone II of China. First, the semidwarfing genes Rht-B1b and Rht-D1b (mutant alleles) conferring to grain yield were analysed. The frequencies of favourable alleles Rht-B1b and Rht-D1b were 32.4 and 58.8%, respectively. Comparing with the previous report, the frequency of Rht-B1b among cultivars in this study is similar to the frequency among cultivars released in the 1990s, while the frequency of Rht-D1b is slightly lower than the previous report 63.9%. Twelve (11.8%) cultivars neither contained Rht-B1b nor Rht-D1b, while only Yumai 66 contained both semidwarfing genes. Linyuan8 and Xinong 928 are heterozygous at RhtB1 locus and Zhengmai 9023 is heterozygous at both RhtB1 and Rht-D1 loci. Second, the TaCwi-A1, TaSus2-2B and TaGW2-6A genes considered as candidate genes related to grain weight were detected. We found that the frequencies of the favourable alleles were 76.5, 56.9 and 69.6%, respectively. Among the 102 wheat varieties, 30 contained all the three favourable genes, 45 contained two of the three favourable genes and 27 contained only one. There are eight wheat varieties (7.8%) in hybrid state at the TaCWI-A1 locus. Third, the designed FM linked to water-saving gene Dreb-B1 were validated on 102 wheat varieties. The results showed that the haplotypes of 47 wheat varieties at the Dreb-B1 locus were same as that of Opata 85, and 55 wheat varieties showed the signal expected for W7984 (Opata 85 and W7984 are parents of the ITMI mapping population). This information will be useful for the wheat breeding programmes aiming at improving yield and water use efficiency in Shijiazhuang located in China Zone II.

A phosphate starvation response regulator Ta-PHR1 is involved in phosphate signalling and increases grain yield in wheat.

BACKGROUND AND AIMS: Phosphorus deficiency is a major limiting factor for crop yield worldwide. Previous studies revealed that PHR1 and it homologues play a key role in regulating the phosphate starvation response in plants. However, the function of PHR homologues in common wheat (Triticum aestivum) is still not fully understood. The aim of the study was to characterize the function of PHR1 genes in regulating phosphate signalling and plant growth in wheat. METHODS: Wheat transgenic lines over-expressing a wheat PHR1 gene were generated and evaluated under phosphorus-deficient and -sufficient conditions in hydroponic culture, a soil pot trial and two field experiments. KEY RESULTS: Three PHR1 homologous genes Ta-PHR1-A1, B1 and D1 were isolated from wheat, and the function of Ta-PHR1-A1 was analysed. The results showed that Ta-PHR1-A1 transcriptionally activated the expression of Ta-PHT1.2 in yeast cells. Over-expressing Ta-PHR1-A1 in wheat upregulated a subset of phosphate starvation response genes, stimulated lateral branching and improved phosphorus uptake when the plants were grown in soil and in nutrient solution. The data from two field trials demonstrated that over-expressing Ta-PHR1-A1 increased grain yield by increasing grain number per spike. CONCLUSIONS: TaPHR1 is involved in phosphate signalling in wheat, and was valuable in molecular breeding of crops, with improved phosphorus use efficiency and yield performance.