Multi-omics approaches investigate the bitter flavor in the shoot of Bambusa oldhamii Munro.

backgroundBamboo, widely distributed in Southeast Asian and East Asia, is a palatable food resource, with its nutritional and low-fat properties, and functions in economic and ecological balance. As an important food source, some bamboo shoots often synthesize bitter chemicals in a special developing period or in a particular position of the shoot, which depends on the edible bamboo species. In this research, we focus on a sympodium bamboo, Bambusa oldhamii Munro, located in Southeast China, which has special biological properties. When the shoots are harvested underground, the shoots taste tender and tasty enough, but when the shoots erupt out of the soil surface with sunlight for days, the shoot has a little bitterness in the tip portion. This research conducts multi-omics approaches to investigate the bitter flavor formation with multiple developing phases of the shoot in B. oldhamii Munro.

resultsThe PacBio and Hi-C technologies were used to sequence the hexaploid species, B. oldhamii Munro, for de novo genome assembly. The assembled genome size of B. oldhamii is 1,446 Mb, with a scaffold-level N50 equal to 38,936,033 bp. A total of 88,140 genes in the genome were acquired, and about 53.89% of the genome is occupied by repeat components. The BUSCO score is 96.59%, suggesting a relatively complete and reliable assembly. Three subgenomes (ABC) include 35 pseudo-chromosomes based on the synteny analysis with another hexaploid species, Dendrocalamus latiflorus. The technologies of transcriptome analysis on the genome level and widely targeted metabolome were used to classify the key transcription factors and key bitter metabolites that account for the bamboo shoot flavor transition of B. oldhamii from underground to above ground, especially in the multiple developing phases. We finally mined out several bitter metabolites belonging to amino acids, flavonoids, terpenoids, purines, and other families, and several related pathways of Circadian rhythm, plant hormone signal transduction, flavonoid biosynthesis, and flavone and flavonol biosynthesis. Additionally, from joint analysis between bitter metabolites and transcription factors, we found that the family of bHLH and HB- transcription factors might influence the shoot bitter flavor transition and formation via influencing the accumulation of bitter metabolites in B. oldhamii.

conclusionsIn this research, we used Multi-omics methods to investigate the bitter flavor formation and transition in the shoot of B. oldhamii and hypothesized a simple model about this biological process. In a suitable circumstance (warm temperature and sunlight), the environment signals transduction influences the expression of transcription factor (bHLH, HB-, and others) which activate or suppress the expression level of genes or enzymes in the bitter flavor metabolites related pathways (biosynthesis of secondary metabolites, amino acid metabolism, biosynthesis of flavonoid, flavone, flavonol and isoflavonoid, plant hormone signal transduction and others), then causing the contents of bitter flavor metabolites (flavonoids, amino acids, terpenoids, cyanogenic glycosides and others) increase or decrease. This phenomenon influences the bitter flavor formation or transition in the shoot of B. oldhamii.