A single base change at exon of Wx-A1 caused gene inactivation and starch properties modified in a wheat EMS mutant line

Reducing amylose content in wheat (Triticum aestivum L.) using a novel Wx-D1 null allele generated by chemical mutagenesis

BACKGROUND

Amylose has a major influence over starch properties and end-use quality in wheat. The granule-bound starch synthase I, encoded by Wx-1, is the single enzyme responsible for amylose synthesis. Natural null mutants of Wx-1 appear at extremely low frequencies, particularly in the Wx-D1 locus, where only four spontaneous null variants have been identified, with different geographic origins. The current study identified an induced Wx-D1 null mutant (M4-9484) from the M4 generation of an ethyl methanesulfonate-mutagenized population of wheat cv. 'SM126'.

RESULTS

The sequencing showed that the complete Wx-D1 ORF sequences of 'SM126' and M4-9484 were 2862 bp long and that there was one SNP mutation between them. The mutation was located at the RNA splice site within the junction of exon 8 and intron 8, which led to abnormal transcription of Wx-D1, with five different aberrant transcripts being identified in the mutant. The Wx-D1 null allele resulted in amylose and total starch content being decreased in M4-9484 in comparison with the wild-type 'SM126', with higher swelling capacity and being fully pasted at higher temperatures than the wild-type parent.

CONCLUSION

The mutation of the Wx-D1 null gene affects the formation of amylose directly, resulting in significantly altered starch properties. This discovery offers valuable insights for enhancing wheat starch quality and contributes to the diversification of starch characteristics. It also deepens our understanding of the genetic and molecular mechanisms underlying amylose synthesis, thereby supporting breeding programs. © 2024 Society of Chemical Industry.

Wheat end-use quality: State of art, genetics, genomics-assisted improvement, future challenges, and opportunities

Wheat is the most important source of food, feed, and nutrition for humans and livestock around the world. The expanding population has increasing demands for various wheat products with different quality attributes requiring the development of wheat cultivars that fulfills specific demands of end-users including millers and bakers in the international market. Therefore, wheat breeding programs continually strive to meet these quality standards by screening their improved breeding lines every year. However, the direct measurement of various end-use quality traits such as milling and baking qualities requires a large quantity of grain, traits-specific expensive instruments, time, and an expert workforce which limits the screening process. With the advancement of sequencing technologies, the study of the entire plant genome is possible, and genetic mapping techniques such as quantitative trait locus mapping and genome-wide association studies have enabled researchers to identify loci/genes associated with various end-use quality traits in wheat. Modern breeding techniques such as marker-assisted selection and genomic selection allow the utilization of these genomic resources for the prediction of quality attributes with high accuracy and efficiency which speeds up crop improvement and cultivar development endeavors. In addition, the candidate gene approach through functional as well as comparative genomics has facilitated the translation of the genomic information from several crop species including wild relatives to wheat. This review discusses the various end-use quality traits of wheat, their genetic control mechanisms, the use of genetics and genomics approaches for their improvement, and future challenges and opportunities for wheat breeding.

HvGBSSI mutation at the splicing receptor site affected RNA splicing and decreased amylose content in barley

Granule-bound starch synthase I (HvGBSSI) is encoded by the barley waxy (Wx-1) gene and is the sole enzyme in the synthesis of amylose. Here, a Wx-1 mutant was identified from an ethyl methane sulfonate (EMS)-mutagenized barley population. There were two single-base mutations G1086A and A2424G in Wx-1 in the mutant (M2-1105). The G1086A mutation is located at the 3' splicing receptor (AG) site of the fourth intron, resulting in an abnormal RNA splicing. The A2424G mutation was a synonymous mutation in the ninth intron. The pre-mRNA of Wx-1 was incorrectly spliced and transcribed into two abnormal transcripts. The type I transcript had a 6 bp deletion in the 5' of fifth exon, leading to a translated HvGBSSI protein lacking two amino acids with a decreased starch-binding capacity. In the type II transcript, the fourth intron was incorrectly cleaved and retained, resulting in the premature termination of the barley Wx-1 gene. The mutations in the Wx-1 decreased the enzymatic activity of the HvGBSSI enzyme and resulted in a decreased level in amylose content. This work sheds light on a new Wx-1 gene inaction mechanism.

Screening of Induced Mutants Led to the Identification of Starch Biosynthetic Genes Associated with Improved Resistant Starch in Wheat

Several health benefits are obtained from resistant starch, also known as healthy starch. Enhancing resistant starch with genetic modification has huge commercial importance. The variation of resistant starch content is narrow in wheat, in relation to which limited improvement has been attained. Hence, there is a need to produce a wheat population that has a wide range of variations in resistant starch content. In the present study, stable mutants were screened that showed significant variation in the resistant starch content. A megazyme kit was used for measuring the resistant starch content, digestible starch, and total starch. The analysis of variance showed a significant difference in the mutant population for resistant starch. Furthermore, four diverse mutant lines for resistant starch content were used to study the quantitative expression patterns of 21 starch metabolic pathway genes; and to evaluate the candidate genes for resistant starch biosynthesis. The expression pattern of 21 starch metabolic pathway genes in two diverse mutant lines showed a higher expression of key genes regulating resistant starch biosynthesis (GBSSI and their isoforms) in the high resistant starch mutant lines, in comparison to the parent variety (J411). The expression of SBEs genes was higher in the low resistant starch mutants. The other three candidate genes showed overexpression (BMY, Pho1, Pho2) and four had reduced (SSIII, SBEI, SBEIII, ISA3) expression in high resistant starch mutants. The overexpression of AMY and ISA1 in the high resistant starch mutant line JE0146 may be due to missense mutations in these genes. Similarly, there was a stop_gained mutation for PHO2; it also showed overexpression. In addition, the gene expression analysis of 21 starch metabolizing genes in four different mutants (low and high resistant starch mutants) shows that in addition to the important genes, several other genes (phosphorylase, isoamylases) may be involved and contribute to the biosynthesis of resistant starch. There is a need to do further study about these new genes, which are responsible for the fluctuation of resistant starch in the mutants.