The origin, evolution and functional divergence of HOOKLESS1 in plants

CsHLS1-CsSCL28 module regulates compact plant architecture in cucumber

Increased planting densities boost crop yields. A compact plant architecture facilitates dense planting. However, the mechanisms regulating compact plant architecture in cucurbits remain unclear. In this study, we identified a cucumber (Cucumis sativus) compact plant architecture (cpa1) mutant from an ethyl methane sulfonate (EMS)-mutagenized library that exhibited distinctive phenotypic traits, including reduced leaf petiole angle and leaf size. The candidate mutation causes a premature stop codon in CsaV3_1G036420, which shares similarity to Arabidopsis HOOKLESS 1 (HLS1) encoding putative histone N-acetyltransferase (HAT) protein and was named CsHLS1. Consistent with the mutant phenotype, CsHLS1 was predominantly expressed in leaf petiole bases and leaves. Constitutive overexpressing CsHLS1 in cpa1 restored the wild-type plant architecture. Knockout of CsHLS1 resulted in reduces leaf petiole angle and leaf size and as well as decreased acetylation levels. Furthermore, CsHLS1 directly interacted with CsSCL28 and negatively regulated compact plant architecture in cucumber. Importantly, CsHLS1 knockout increased the photosynthesis rate and leaf nitrogen in cucumbers, thereby maintaining cucumber yield at normal density. Overall, our research provides valuable genetic breeding resource and gene target for creating a compact plant architecture for dense cucumber planting.

Natural Allelic Variations of Bch10G006400 Controlling Seed Size in Chieh-qua (Benincasa hispida Cogn. var. Chieh-qua How)

Seeds are the most important reproductive organs of higher plants, the beginning and end of a plant's lifecycle. They are very important to plant growth and development, and also an important factor affecting yield. In this study, genetic analysis and BSA-seq of the F2 population crossed with the large-seeded material 'J16' and small-seeded material 'FJ5' were carried out, and the seed size locus was initially located within the 1.31 Mb region on chr10. In addition, 2281 F2 plants were used to further reduce the candidate interval to 48.8 Kb. This region contains only one gene encoding the N-acetyltransferase (NAT) protein (Bch10G006400). Transcriptome and expression analysis revealed that the gene was significantly more highly expressed in 'J16' than in 'FJ5'. Variation analysis of Bch10G006400 among parents and 50 chieh-qua germplasms revealed that as well as a nonsynonymous mutation (SNP_314) between parents, two mutations (SNP_400 and InDel_551) were detected in other materials. Combining these three mutations completely distinguished the seed size of the chieh-qua. GO and KEGG enrichment analyses revealed that DGEs played the most important roles in carbohydrate metabolism and plant hormone signal transduction, respectively. The results of this study provide important information for molecular marker-assisted breeding and help to reveal the molecular mechanism of seed size.

A nonsynonymous mutation in BhLS, encoding an acyl-CoA N-acyltransferase leads to fruit and seed size variation in wax gourd (Benincasa hispida)

Wax gourd (Benincasa hispida (Thunb.) Cogn., 2n = 2x = 24) is an economically important vegetable crop cultivated widely in many tropical and subtropical regions, including China, India, and Japan. Both fruit and seeds are prized agronomic attributes in wax gourd breeding and production. However, the genetic mechanisms underlying these traits remain largely unexplored. In this study, we observed a strong correlation between fruit size and seed size variation in our mapping population, indicating genetic control by a single gene, BhLS, with large size being dominant over small. Through bulk segregant analysis sequencing and fine mapping with a large F2 population, we precisely located the BhLS gene within a 47.098-kb physical interval on Chromosome 10. Within this interval, only one gene, Bhi10M000649, was identified, showing homology to Arabidopsis HOOKLESS1. A nonsynonymous mutation (G to C) in the second exon of Bhi10M000649 was found to be significantly associated with both fruit and seed size variation in wax gourd. These findings collectively highlight the pleiotropic effect of the BhLS gene in regulating fruit and seed size in wax gourd. Our results offer molecular insights into the variation of fruit and seed size in wax gourd and establish a fundamental framework for breeding wax gourd cultivars with desired traits.

Fine mapping of the major gene BhHLS1 controlling seed size in wax gourd (Benincasa hispida)

Introduction/Background

The seed size of wax gourds is an important agronomic trait; however, the associated genes have not yet been reported.

Methods

In this study, we used a high-density genetic map constructed based on F8 recombinant inbred line populations derived from a cross between MY-1 (large seed) and GX-71 (small seed) strains to detect quantitative trait locis (QTLs) for seed-size-related traits in wax gourd over a two-year period.

Results

Two stable QTLs (qSL10 and qSW10) for seed length (SL) and seed width (SW) on chromosome 10 were repeatedly detected over two years (2021-2022). qSL10 had a phenotypic variation rate of 75.30% and 80.80% in 2021 and 2022, respectively. Whereas, qSW10 had a phenotypic variation rate of 66.60% and 73.80% in 2021 and 2022, respectively. Further, a single nucleotide polymorphism mutation was found to cause early termination of Bch10G006400 (BhHLS1) translation in GX-71 through sequencing analysis of candidate genes. Based on gene functional annotation and quantitative real-time PCR analyses, BhHLS1 encoded a probable N-acetyltransferase HLS1-like protein and its expression level was significantly different between parents. Therefore, BhHLS1 is a major candidate gene associated with a one-factor polymorphism regulating the SL and SW of wax gourds. Finally, based on variation in the BhHLS1 sequence, a cleaved amplified polymorphic sequence marker was developed for the molecular marker-assisted breeding of wax gourds.

Discussion

Overall, this study is of great significance for the genetic improvement of seed size, verification of gene functions, and cultivation of specific germplasm resources for wax gourds.