QTL mapping and transcriptome analysis identify candidate genes regulating pericarp thickness in sweet corn.

BACKGROUND: In recent years, the planting area of sweet corn in China has expanded rapidly. Some new varieties with high yields and good adaptabilities have emerged. However, the improvement of edible quality traits, especially through the development of varieties with thin pericarp thickness, has not been achieved to date. Pericarp thickness is a complex trait that is the key factor determining the edible quality of sweet corn. Genetic mapping combined with transcriptome analysis was used to identify candidate genes controlling pericarp thickness. RESULTS: To identify novel quantitative trait loci (QTLs) for pericarp thickness, a sweet corn BC4F3 population of 148 lines was developed using the two sweet corn lines M03 (recurrent parent) and M08 (donor parent). Additionally, a high-density genetic linkage map containing 3876 specific length amplified fragment (SLAF) tags was constructed and used for mapping QTLs for pericarp thickness. Interestingly, 14 QTLs for pericarp thickness were detected, and one stable QTL (qPT10-5) was detected across multiple years, which explained 7.78-35.38% of the phenotypic variation located on chromosome 10 (144,631,242-145,532,401). Forty-two candidate genes were found within the target region of qPT10-5. Moreover, of these 42 genes, five genes (GRMZM2G143402, GRMZM2G143389, GRMZM2G143352, GRMZM6G287947, and AC234202.1_FG004) were differentially expressed between the two parents, as revealed by transcriptome analysis. According to the gene annotation information, three genes might be considered candidates for pericarp thickness. GRMZM2G143352 and GRMZM2G143402 have been annotated as AUX/IAA transcription factor and ZIM transcription factor, respectively, while GRMZM2G143389 has been annotated as FATTY ACID EXPORT 2, chloroplastic. CONCLUSIONS: This study identified a major QTL and candidate genes that could accelerate breeding for the thin pericarp thickness variety of sweet corn, and these results established the basis for map-based cloning and further functional research.

Transcriptome analysis reveals ZmERF055 contributes to waterlogging tolerance in sweetcorn.

Waterlogging is a major disaster damaging crop production. However, most sweetcorn cultivars are not tolerant to waterlogging, which severely threatens their production. In order to understand the genetic mechanisms underlying waterlogging tolerance in sweetcorn, this study conducted a comprehensive investigation of sweetcorn waterlogging tolerance at the levels of physiology, biochemistry, and transcriptome in two sweetcorn CSSLs (chromosome segment substitution lines), D120 and D81. We found that D120 showed increased plant height, root length, root area, adventitious root numbers, antioxidant enzyme activities, and aerenchyma area ratio compared to D81. The transcriptome results showed that 2492 and 2351 differentially expressed genes (DEGs) were obtained at 4 h and 8 h of waterlogging treatment, respectively. Genes involved in reactive oxygen species (ROS) homeostasis, photosynthesis, and alcohol fermentation are sensitive in the waterlogging tolerant genotype D120, resulting in enhanced ROS scavenging ability, adventitious roots, and aerenchyma formation. Additionally, ethylene-, auxin-, and ABA-related genes exhibited different responses to waterlogging stress in sweetcorn. We integrated transcriptome and differential chromosomal fragments data and identified that ZmERF055 on chromosome 9 was directly involved in waterlogging stress. ZmERF055-overexpressing plants consistently exhibited significantly increased waterlogging tolerance and ROS homeostasis in Arabidopsis. These results offer a network of plant hormone signaling, ROS homeostasis, and energy metabolism co-modulating waterlogging tolerance in sweetcorn. Additionally, the findings support ZmERF055 as a potential ideal target gene in crop breeding to improve plant waterlogging tolerance.

Integration of miRNA and mRNA analysis reveals the role of ribosome in to anti-artificial aging in sweetcorn.

Sweetcorn is a kind of maize with high sugar content and has poor seed aging tolerance, which seriously limits its production. However, few studies have explored the artificial aging (AA) tolerance by miRNA-mRNA integration analysis in sweetcorn. Here, we characterized the physiological, biochemical and transcriptomic changes of two contrasting lines K62 and K107 treated with AA during time series. Both the germination indexes and antioxidant enzymes showed significant difference between two lines. The MDA content of AA-tolerant genotype K62 was significantly lower than that of K107 on the fourth and sixth day. Subsequently, 157 differentially expressed miRNAs (DEMIs) and 8878 differentially expressed mRNAs (DEMs) were identified by RNA-seq analysis under aging stress. The "ribosome" and "peroxisome" pathways were enriched to respond to aging stress, genes for both large units and small ribosomal subunits were significantly upregulated expressed and higher translation efficiency might exist in K62. Thirteen pairs of miRNA-target genes were obtained, and 8 miRNA-mRNA pairs might involve in ribosome protein and translation process. Our results elucidate the mechanism of sweetcorn response to AA at miRNA-mRNA level, and provide a new insight into sweetcorn AA response to stress.

Construction of High-Density Genetic Map and Identification of QTLs Associated with Seed Vigor after Exposure to Artificial Aging Conditions in Sweet Corn Using SLAF-seq.

Seed vigor is a key factor that determines the quality of seeds, which is of great significance for agricultural production, with the potential to promote growth and productivity. However, the underlying molecular mechanisms and genetic basis for seed vigor remain unknown. High-density genetic linkage mapping is an effective method for genomic study and quantitative trait loci (QTL) mapping. In this study, a high-density genetic map was constructed from a 148 BC4F3 population cross between 'M03' and 'M08' strains based on specific-locus amplified fragment (SLAF) sequencing. The constructed high-density genetic linkage map (HDGM) included 3876 SNP markers on ten chromosomes covering 2413.25 cM in length, with a mean distance between markers of 0.62 cM. QTL analysis was performed on four sweet corn germination traits that are related to seed vigor under artificial aging conditions. A total of 18 QTLs were identified in two seasons. Interestingly, a stable QTL was detected in two seasons on chromosome 10-termed qGR10-within an interval of 1.37 Mb. Within this interval, combined with gene annotation, we found four candidate genes (GRMZM2G074309, GRMZM2G117319, GRMZM2G465812, and GRMZM2G343519) which may be related to seed vigor after artificial aging.