Changes in volatile profile and related gene expression during senescence of tobacco leaves

BACKGROUND

Volatile organic compounds are critical for food flavor and play important roles in plant-plant interactions and plants' communications with the environment. Tobacco is well-studied for secondary metabolism and most of the typical flavor substances in tobacco leaves are generated at the mature stage of leaf development. However, the changes in volatiles during leaf senescence are rarely studied.

RESULTS

The volatile composition of tobacco leaves at different stages of senescence was characterized for the first time. Comparative volatile profiling of tobacco leaves at different stages was performed using solid-phase microextraction coupled with gas chromatography/mass spectrometry. In total, 45 volatile compounds were identified and quantified, including terpenoids, green leaf volatiles (GLVs), phenylpropanoids, Maillard reaction products, esters, and alkanes. Most of the volatile compounds showed differential accumulation during leaf senescence. Some terpenoids, including neophytadiene, β-springene, and 6-methyl-5-hepten-2-one, increased significantly with the progress of leaf senescence. Hexanal and phenylacetaldehyde also showed increased accumulation in leaves during senescence. The results from gene expression profiling indicated that genes involved in metabolism of terpenoids, phenylpropanoids, and GLVs were differentially expressed during leaf yellowing.

CONCLUSION

Dynamic changes in volatile compounds during tobacco leaf senescence are observed and the integration of gene-metabolites datasets offers important readouts for the genetic control of volatile production during the process of leaf senescence. © 2023 Society of Chemical Industry.

Formation of α- and β-Cembratriene-Diols in Tobacco (Nicotiana tabacum L.) Is Regulated by Jasmonate-Signaling Components via Manipulating Multiple Cembranoid Synthetic Genes

Cembranoids are a group of natural diterpenoid compounds with pharmaceutical potentials, and the cembratriene-diols produced by Nicotiana (tobacco) species display activities in anti-nicotine addiction and neuron protection. Although the enzymes catalyzing cembratriene-diols' formation in tobacco have been investigated, the regulatory mechanism underlying this physiological process remains unknown. This study has investigated the roles of phytohormone jasmonic acid (JA) in regulating cembratriene-diol formation in N. tabacum cv. TN90 and found that JA and COI1, the receptor protein of the bioactive derivative of JA (i.e., JA-Ile), display critical roles in regulating cembratriene-diols' formation and the expression of cembranoid synthetic genes CBTS, P450 and NtLTP1. Further studies showed that over-expressing either the gene encoding bHLH transcription factor MYC2a or that encoding MYB transcription factor MYB305 could upregulate the cembranoid synthetic genes and enhance the cembranoid production in plants with dysfunction of COI1. Further studies suggest that COI1 and its downstream regulators MYC2a and MYB305 also modulate the trichome secretion, which is correlated with cembranoid formation. Taken together, this study has demonstrated a critical role of JA-signaling components in governing the cembratriene-diol formation and the transcription of cembratriene-diol synthetic genes in tobacco. Findings in this study are of great importance to reveal the molecular regulatory mechanism underlying cembranoid synthesis.

Development of a maize 55 K SNP array with improved genome coverage for molecular breeding

With the decrease of cost in genotyping, single nucleotide polymorphisms (SNPs) have gained wide acceptance because of their abundance, even distribution throughout the maize (Zea mays L.) genome, and suitability for high-throughput analysis. In this study, a maize 55 K SNP array with improved genome coverage for molecular breeding was developed on an Affymetrix® Axiom® platform with 55,229 SNPs evenly distributed across the genome, including 22,278 exonic and 19,425 intronic SNPs. This array contains 451 markers that are associated with 368 known genes and two traits of agronomic importance (drought tolerance and kernel oil biosynthesis), 4067 markers that are not covered by the current reference genome, 734 markers that are differentiated significantly between heterotic groups, and 132 markers that are tags for important transgenic events. To evaluate the performance of 55 K array, we genotyped 593 inbred lines with diverse genetic backgrounds. Compared with the widely-used Illumina® MaizeSNP50 BeadChip, our 55 K array has lower missing and heterozygous rates and more SNPs with lower minor allele frequency (MAF) in tropical maize, facilitating in-depth dissection of rare but possibly valuable variation in tropical germplasm resources. Population structure and genetic diversity analysis revealed that this 55 K array is also quite efficient in resolving heterotic groups and performing fine fingerprinting of germplasm. Therefore, this maize 55 K SNP array is a potentially powerful tool for germplasm evaluation (including germplasm fingerprinting, genetic diversity analysis, and heterotic grouping), marker-assisted breeding, and primary quantitative trait loci (QTL) mapping and genome-wide association study (GWAS) for both tropical and temperate maize.