Preharvest sprouting and α-amylase activity in soft winter wheat

A wheat heat shock transcription factor gene, TaHsf-7A, regulates seed dormancy and germination

Heat shock transcription factors (Hsfs) play multifaceted roles in plant growth, development, and responses to environmental factors. However, their involvement in seed dormancy and germination processes has remained elusive. In this study, we identified a wheat class B Hsf gene, TaHsf-7A, with higher expression in strong-dormancy varieties compared to weak-dormancy varieties during seed imbibition. Specifically, TaHsf-7A expression increased during seed dormancy establishment and subsequently declined during dormancy release. Through the identification of a 1-bp insertion (ins)/deletion (del) variation in the coding region of TaHsf-7A among wheat varieties with different dormancy levels, we developed a CAPS marker, Hsf-7A-1319, resulting in two allelic variations: Hsf-7A-1319-ins and Hsf-7A-1319-del. Notably, the allele Hsf-7A-1319-ins correlated with a reduced seed germination rate and elevated dormancy levels, while Hsf-7A-1319-del exhibited the opposite trend across 175 wheat varieties. The association of TaHsf-7A allelic status with seed dormancy and germination levels was confirmed in various genetically modified species, including Arabidopsis, rice, and wheat. Results from the dual luciferase assay demonstrated notable variations in transcriptional activity among transformants harboring distinct TaHsf-7A alleles. Furthermore, the levels of abscisic acid (ABA) and gibberellin (GA), along with the expression levels of ABA and GA biosynthesis genes, showed significant differences between transgenic rice lines carrying different alleles of TaHsf-7A. These findings represent a significant step towards a comprehensive understanding of TaHsf-7A's involvement in the dormancy and germination processes of wheat seeds.

Regulatory function of the endogenous hormone in the germination process of quinoa seeds

The economic and health significance of quinoa is steadily growing on a global scale. Nevertheless, the primary obstacle to achieving high yields in quinoa cultivation is pre-harvest sprouting (PHS), which is intricately linked to seed dormancy. However, there exists a dearth of research concerning the regulatory mechanisms governing PHS. The regulation of seed germination by various plant hormones has been extensively studied. Consequently, understanding the mechanisms underlying the role of endogenous hormones in the germination process of quinoa seeds and developing strategies to mitigate PHS in quinoa cultivation are of significant research importance. This study employed the HPLC-ESI-MS/MS internal standard and ELISA method to quantify 8 endogenous hormones. The investigation of gene expression changes before and after germination was conducted using RNA-seq analysis, leading to the discovery of 280 differentially expressed genes associated with the regulatory pathway of endogenous hormones. Additionally, a correlation analysis of 99 genes with significant differences identified 14 potential genes that may act as crucial "transportation hubs" in hormonal interactions. Through the performance of an analysis on the modifications in hormone composition and the expression of associated regulatory genes, we posit a prediction that implies the presence of a negative feedback regulatory mechanism of endogenous hormones during the germination of quinoa seeds. This mechanism is potentially influenced by the unique structure of quinoa seeds. To shed light on the involvement of endogenous hormones in the process of quinoa seed germination, we have established a regulatory network. This study aims to offer innovative perspectives on the breeding of quinoa varieties that exhibit resistance to PHS, as well as strategies for preventing PHS.

Genetic Improvement of Wheat with Pre-Harvest Sprouting Resistance in China

Wheat pre-harvest sprouting (PHS) refers to the germination of seeds directly on the spike due to rainy weather before harvest, which often results in yield reduction, quality deterioration, and seed value loss. In this study, we reviewed the research progress in the quantitative trait loci (QTL) detection and gene excavation related to PHS resistance in wheat. Simultaneously, the identification and creation of germplasm resources and the breeding of wheat with PHS resistance were expounded in this study. Furthermore, we also discussed the prospect of molecular breeding during genetic improvement of PHS-resistant wheat.

Allelic Variations in Phenology Genes of Eastern U.S. Soft Winter and Korean Winter Wheat and Their Associations with Heading Date

Wheat heading time is genetically controlled by phenology genes including vernalization (Vrn), photoperiod (Ppd) and earliness per se (Eps) genes. Characterization of the existing genetic variation in the phenology genes of wheat would provide breeding programs with valuable genetic resources necessary for the development of wheat varieties well-adapted to the local environment and early-maturing traits suitable for double-cropping system. One hundred forty-nine eastern U.S. soft winter (ESW) and 32 Korean winter (KW) wheat genotypes were characterized using molecular markers for Vrn, Ppd, Eps and reduced-height (Rht) genes, and phenotyped for heading date (HD) in the eastern U.S. region. The Ppd-D1 and Rht-D1 genes exhibited the highest genetic diversity in ESW and KW wheat, respectively. The genetic variations for HD of ESW wheat were largely contributed by Ppd-B1, Ppd-D1 and Vrn-D3 genes. The Rht-D1 gene largely contributed to the genetic variation for HD of KW wheat. KW wheat headed on average 14 days earlier than ESW wheat in each crop year, largely due to the presence of the one-copy vrn-A1 allele in the former. The development of early-maturing ESW wheat varieties could be achieved by selecting for the one-copy vrn-A1 and vrn-D3a alleles in combination with Ppd-B1a and Ppd-D1a photoperiod insensitive alleles.

Pre-harvest sprouting in cereals: genetic and biochemical mechanisms

With the growth of the global population and the increasing frequency of natural disasters, crop yields must be steadily increased to enhance human adaptability to risks. Pre-harvest sprouting (PHS), a term mainly used to describe the phenomenon in which grains germinate on the mother plant directly before harvest, is a serious global problem for agricultural production. After domestication, the dormancy level of cultivated crops was generally lower than that of their wild ancestors. Although the shortened dormancy period likely improved the industrial performance of cereals such as wheat, barley, rice, and maize, the excessive germination rate has caused frequent PHS in areas with higher rainfall, resulting in great economic losses. Here, we systematically review the causes of PHS and its consequences, the major indicators and methods for PHS assessment, and emphasize the biological significance of PHS in crop production. Wheat quantitative trait loci functioning in the control of PHS are also comprehensively summarized in a meta-analysis. Finally, we use Arabidopsis as a model plant to develop more complete PHS regulatory networks for wheat. The integration of this information is conducive to the development of custom-made cultivated lines suitable for different demands and regions, and is of great significance for improving crop yields and economic benefits.

Identification of the wheat C3H gene family and expression analysis of candidates associated with seed dormancy and germination

C3H zinc finger transcription factors play important roles in managing various biotic/abiotic stresses in Aarabidopsis, rice, and maize. The functions of these factors in wheat, however, remain largely unclear. We identified 88 TaC3H genes that were divided into four subfamilies in this analysis. Gene structure and conserved domain analyses indicate that most members of the same subfamily have similar structures. A total of 76 paralogous and 48 orthologous pairs were identified and Ka/Ks values were used to analyze replication relationships amongst wheat, rice, and Arabidopsis. Gene ontology (GO) annotation analysis showed that most TaC3H genes possessed molecular functions, while transcriptome results showed that the 88 TaC3H genes responded to water imbibition. Microarray data for 53 TaC3H genes were obtained and heat maps were generated; these results indicate that these genes are expressed in 13 wheat tissues. Subcellular localization prediction analysis indicates that most TaC3H genes are located in the nucleus. Promoter analysis indicates that most TaC3H genes contained cis-elements including ABRE, GARE-motif, and MBS, indicating that these can respond to various biotic/abiotic stresses. Transcriptome data and quantitative real-time PCR analysis of wheat cultivars with contrasting seed dormancy phenotypes show that five genes TaC3H4/-18/-37/-51/-72 were very likely involved in seed dormancy and germination. Exogenous ABA treatment further indicated that these five genes were responsive to ABA, suggesting that there may be a crosstalk between these genes and ABA signaling pathway in controlling seed dormancy and germination. These results provide a theoretical basis for subsequent studies on TaC3H gene function and also contribute to studies on the C3H gene in other species.

Genome-wide association study of pre-harvest sprouting tolerance using a 90K SNP array in common wheat (Triticum aestivum L.)

Three major loci for pre-harvest sprouting tolerance (PHST) were mapped on chromosomes 1AL, 3BS, and 6BL, and two CAPS and one dCAPS markers were validated. Sixteen lines with favorable alleles and increased PHST were identified. Pre-harvest sprouting (PHS) significantly affects wheat grain yield and quality. In the present study, the PHS tolerance (PHST) of 192 wheat varieties (lines) was evaluated by assessment of field sprouting, seed germination index, and period of dormancy in different environments. A high-density Illumina iSelect 90K SNP array was used to genotype the panel. A genome-wide association study (GWAS) based on single- and multi-locus mixed linear models was used to detect loci for PHST. The single-locus model identified 23 loci for PHST (P < 0.0001) and explained 6.0-18.9% of the phenotypic variance. Twenty loci were consistent with known quantitative trait loci (QTLs). Three single-nucleotide polymorphism markers closely linked with three major loci (Qphs.ahau-1A, Qphs.ahau-3B, and Qphs.ahau-6B) on chromosomes 1AL, 3BS, and 6BL, respectively, were converted to two cleaved amplified polymorphic sequences (CAPS) and one derived-CAPS markers, and validated in 374 wheat varieties (lines). The CAPS marker EX06323 for Qphs.ahau-6B co-segregated with a novel major QTL underlying PHST in a recombinant inbred line population raised from the cross Jing 411 × Wanxianbaimaizi. Linear regression showed a clear dependence of PHST on the number of favorable alleles. Sixteen varieties showing an elevated degree of PHST were identified and harbored more than 16 favorable alleles. The multi-locus model detected 39 marker-trait associations for PHST (P < 0.0001), of which five may be novel. Six loci common to the two models were identified. The combination of the two GWAS methods contributes to efficient dissection of the complex genetic mechanism of PHST.

Identification and Analysis of the GASR Gene Family in Common Wheat (Triticum aestivum L.) and Characterization of TaGASR34, a Gene Associated With Seed Dormancy and Germination

Seed dormancy and germination are important agronomic traits in wheat (Triticum aestivum L.) because they determine pre-harvest sprouting (PHS) resistance and thus affect grain production. These processes are regulated by Gibberellic Acid-Stimulated Regulator (GASR) genes. In this study, we identified 37 GASR genes in common wheat, which were designated TaGASR1-37. Moreover, we identified 40 pairs of paralogous genes, of which only one had a Ka/Ks value greater than 1, indicating that most TaGASR genes have undergone negative selection. Chromosomal location and duplication analysis revealed 25 pairs of segmentally duplicated genes and seven pairs of tandemly duplicated genes, suggesting that large-scale duplication events may have contributed to the expansion of TaGASR gene family. Microarray analysis of the expression of 18 TaGASR genes indicated that these genes play diverse roles in different biological processes. Using wheat varieties with contrasting seed dormancy phenotypes, we investigated the expression patterns of TaGASR genes and the corresponding seed germination index phenotypes in response to water imbibition, exogenous ABA and GA treatment, and low- and high-temperature treatment. Based on these data, we identified the TaGASR34 gene as potentially associated with seed dormancy and germination. Further, we used a SNP mutation of the TaGASR34 promoter (-16) to develop the CAPS marker GS34-7B, which was then used to validate the association of TaGASR34 with seed dormancy and germination by evaluating two natural populations across environments. Notably, the frequency of the high-dormancy GS34-7Bb allele was significantly lower than that of the low-dormancy GS34-7Ba allele, implying that the favorable GS34-7Bb allele has not previously been used in wheat breeding. These results provide valuable information for further functional analysis of TaGASR genes and present a useful gene and marker combination for future improvement of PHS resistance in wheat.