| With the rapid development of China’s cigar industry,the supply of high-quality raw materials for cigar wrapper has become a "bottleneck" issue in the development of the cigar industry.In this study,the growth and development of cigar wrapper tobacco plants and their leaf quality characteristics under different shading treatments(non-shading,shading rate of 20%,and shading rate of 40%)were studied using the cigar wrapper tobacco variety ’Yunxue No.1’ as the experimental material through a combined analysis of transcriptomics and extensive targeted metabolomics.The purpose of this study was to explore the impact of shading treatment on the quality of cigar wrapper tobacco leaves and provide a theoretical basis for directional cultivation of high-quality cigar wrapper tobacco leaves.The main research results are as follows:(1)Cigar wrapper tobacco plants can adapt to shading through morphological and physiological changes.As the degree of shading increased,the plant height,maximum leaf length,leaf width,and pitch increased,and the stem circumference decreased;The total content of chlorophyll a and chlorophyll in tobacco leaves increased,while the content of carotenoids decreased.Compared with non-shading,the antioxidant enzyme activity of cigar wrapper tobacco leaves significantly increased under shading treatment;under the shading rate of 20% and 40%,the content of malondialdehyde significantly decreased by 9.98% and 17.73%,the content of proline significantly increased by 23.49%and 36.96%,and the content of soluble protein significantly decreased by 33.58% and40.84%,respectively(P < 0.05).(2)Shading improved the physical and sensory qualities of cigar wrapper tobacco leaves.Under shading conditions,the physical properties and sensory quality of cigar wrapper tobacco leaves were improved;the sugar and chloride ion content decreased,the total nitrogen and nicotine increased.Among them,the total nitrogen and nicotine content of tobacco leaves significantly increased by 6.93% and 23.60% under the treatment of 40% shading rate(P < 0.05);the potassium content reaches its maximum value when the shading rate is 40%,but the difference is not significant compared to the non shading treatment.(3)Shading affects the biological processes and pathways of the development of cigar wrapper tobacco leaves.GO enrichment analysis showed that shading mainly affects the response of active oxygen levels,fatty acid synthesis,phenylpropanoid synthesis,chitin,and secondary metabolite synthesis related biological processes in cigar wrapper tobacco leaves;The molecular functions mainly include the activities of carbon-carbon lyase,carbon-oxygen lyase,carboxylate ester hydrolase,and glucose transferase.The number of differentially expressed genes enriched in the synthesis pathway of secondary metabolites is the highest,with 484;the second is plant pathogen interaction pathway,endoplasmic reticulum protein processing pathway and plant hormone signal transduction pathway.The number of differentially expressed genes distributed in the biosynthesis of secondary metabolites pathway is the largest.Among the differential expressed metabolites in response to shading treatment in cigar wrapper tobacco leaves,34 species were significantly upregulated,mainly lipids,alkaloids,organic acids,and other substances;there are 96 significantly downregulated substances,mainly flavonoids,phenolic acids,alkaloids,and other substances.These differentially expressed metabolites are also mainly concentrated in the biosynthesis of secondary metabolites pathway.(4)Plant hormone signal transduction pathway is a key pathway for cigar wrapper tobacco leaves to respond to shading.There are 16 metabolic pathways that are coenriched by differentially expressed genes and differentially expressed metabolites,and the significantly enriched pathways are plant hormone signal transduction pathways.The pathway is enriched with 77 upregulated and 25 downregulated genes,which mainly encode 12 regulatory protein families or enzymes such as AUX1,AUX/IAA,ARF,GH3,SAUR,CRE1,B-ARR,A-ARR,BIR1,BSK,BZR1/2 and TCH4;the differentially expressed metabolites are jasmonic acid and jasmonic acid L-isoleucine,both of which are upregulated.In summary,cigar wrapper tobacco plants can adapt to the shading environment by increasing leaf area,chlorophyll content and improving antioxidant capacity,etc.Shading mainly affects the expression of genes and synthesis of metabolites related to the biosynthesis of secondary metabolites and plant hormone signal transduction pathways in cigar wrapper tobacco leaves,thereby affecting the quality factors of tobacco leaves. |
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