Sucrose content is a crucial indicator of quality and flavor in peanut seed, and there is a lack of clarity on the molecular basis of sucrose metabolism in peanut seed. In this context, we performed a comprehensive comparative transcriptome study on the samples collected at seven seed development stages between a high-sucrose content variety (ICG 12625) and a low-sucrose content variety (Zhonghua 10). The transcriptome analysis identified a total of 8334 genes exhibiting significantly different abundances between the high- and low-sucrose varieties. We identified 28 differentially expressed genes (DEGs) involved in sucrose metabolism in peanut and 12 of these encoded sugars will eventually be exported transporters (SWEETs). The remaining 16 genes encoded enzymes, such as cell wall invertase (CWIN), vacuolar invertase (VIN), cytoplasmic invertase (CIN), cytosolic fructose-bisphosphate aldolase (FBA), cytosolic fructose-1,6-bisphosphate phosphatase (FBP), sucrose synthase (SUS), cytosolic phosphoglucose isomerase (PGI), hexokinase (HK), and sucrose-phosphate phosphatase (SPP). The weighted gene co-expression network analysis (WGCNA) identified seven genes encoding key enzymes (CIN, FBA, FBP, HK, and SPP), three SWEET genes, and 90 transcription factors (TFs) showing a high correlation with sucrose content. Furthermore, upon validation, six of these genes were successfully verified as exhibiting higher expression in high-sucrose recombinant inbred lines (RILs). Our study suggested the key roles of the high expression of SWEETs and enzymes in sucrose synthesis making the genotype ICG 12625 sucrose-rich. This study also provided insights into the molecular basis of sucrose metabolism during seed development and facilitated exploring key candidate genes and molecular breeding for sucrose content in peanuts.

Background: Aflatoxin contamination caused by Aspergillus fungi has been a serious factor affecting food safety of peanut (Arachis hypogaea L.) because aflatoxins are highly harmful for human and animal health. As three mechanisms of resistance to aflatoxin in peanut including shell infection resistance, seed infection resistance and aflatoxin production resistance exist among naturally evolved germplasm stocks, it is highly crucial to pyramid these three resistances for promoting peanut industry development and protecting consumers’ health. However, less research effort has been made yet to investigate the differentiation and genetic relationship among the three resistances in diversified peanut germplasm collections. Results: In this study, the Chinese peanut mini-mini core collection selected from a large basic collection was systematically evaluated for the three resistances against A. flavus for the first time. The research revealed a wide variation among the diversified peanut accessions for all the three resistances. Totally, 14 resistant accessions were identified, including three with shell infection resistance, seven with seed infection resistance and five with aflatoxin production resistance. A special accession, Zh.h1312, was identified with both seed infection and aflatoxin production resistance. Among the five botanic types of A. hypogaea, the var. vulgaris (Spanish type) belonging to subspecies fastigiata is the only one which possessed all the three resistances. There was no close correlation between shell infection resistance and other two resistances, while there was a significant positive correlation between seed infection and toxin production resistance. All the three resistances had a significant negative correlation with pod or seed size. A total of 16 SNPs/InDels associated with the three resistances were identified through genome-wide association study (GWAS). Through comparative analysis, Zh.h1312 with seed infection resistance and aflatoxin production resistance was also revealed to possess all the resistance alleles of associated loci for seed infection index and aflatoxin content. Conclusions: This study provided the first comprehensive understanding of differentiation of aflatoxin resistance in diversified peanut germplasm collection, and would further contribute to the genetic enhancement for resistance to aflatoxin contamination.

With the increasing size of edible peanuts market, the quality characteristics of edible peanuts have attracted much attention. Sweetness is an important indicator affecting the flavor and taste of edible peanuts, and it mainly comes from sucrose. Increasing sucrose content is the key to the edible peanuts cultivation, and QTL mapping for sucrose content will lay a foundation for molecular breeding of high sucrose content. However, the increase of sucrose content may affect protein and oil content. In this study, a recombinant inbred line population derived from the cross of Xuhua 13 and Zhonghua 6 was developed. The relationships between sucrose and protein as well as oil content were investigated, and QTLs for sucrose content were mapped. The results showed that sucrose content was not significantly correlated with protein content but there was extremely significantly negatively correlated with the content. Sucrose content presented board phenotypic variations among the RILs, ranging from 14.33 mg g-1 to 61.42 mg g-1. Two lines with high protein, low oil content, and medium sucrose content were observed. Ten QTLs on six chromosomes were detected with 4.56%-12.25% of phenotypic variation explained (PVE) among which qSUCA07 could be repeatedly detected in three environments. The results provide an important information for QTLs fine mapping of sucrose content and cultivating edible peanut varieties with excellent traits.

Peanut is an important source of edible vegetable oil in China, and improving the quality of peanut oil is an important goal in peanut breeding. In this study, the contents of very long-chain saturated fatty acids (arachidic acid, behenic acid, and tetracosanoic acid) were determined by using RIL population containing 140 lines derived from the cross between Zhonghua 10 and ICG12625 with different genetic backgrounds. The content of very long- chain saturated fatty acid in the RILs was 4.27%–7.05%, with an average of 5.54%, the minimum value was 1.46 and 1.63 percentage points lower than that of male and female parents, with reduction rates of 25.27% and 27.62%, respectively. The behenic acid content ranged from 1.86% to 3.37%, with an average of 2.53%. Three lines of QT0002, QT0075, and QT0120 had behenic acid content lower than 2%, which was 0.57, 0.51, and 0.51 percentage points lower than that of Zhonghua10 with the reduction rate of 23.45%, 20.98%, and 20.98%, respectively. A stable QTL located in 13.31–16.34 M of B04 was detected using a linkage map and WinQTLcart software. In this region of 13.31–16.34 M contained 131 prediction genes. The results lay a foundation for the genetic improvement of low behenic acid and high-oleic peanut varieties.