Study On Molecular Mechanism Of Carotenoid Metabolism In Banana Fruit

Bananas(Musa spp.)are popular fruits and major staple crops.Carotenoids are critic for human health.Banana variety with high carotenoid content will value more in international fruit and staple crop market.To lay a theoretical foundation for molecular breeding of high carotenoid content banana cultivar,carotenoid composition and content of 36 banana varieties were studied by HPLC.Two cultivars represent high or low pulp carotenoid content respectively were chosen for further research.Differences of carotenoid accumulation during fruit development and relative expressions of carotenogenic genes in two cultivars were analyzed.TMT quantitative proteomics technology was employed to study the global proteomic difference.The results showed: 1.Analysis of carotenoid content and composition in banana fruitLutein,α-carotene and β-carotene were major carotenoids in banana fruits.Violaxanthin,Neoxanthin,Antheraxanthin,α-Cryptoxanthin and β-Cryptoxanthin were detected in banana peel.Total carotenoid content in banana peel was normally higher than banana pulp.But some banana cultivar had higher carotenoid content in pulp.This phenotype is valuable for molecular breeding.Two varieties,Musa AAA(Cavendish subgroup)’Grand Naine’(low carotenoid content,brief in ’GN’)and Musa AAB(plantain subgroup)’Obubit Ntanga green mutant’(high carotenoid content,brief in ’ON’),were chosen for further research.Carotenoid content in fruits at each developmnet stage were studied.Total carotenoid content of both varieties showed an increasing trend during fruit development.At the last developing stage,difference of carotenoid content was less than 0.2 fold between peel of ’GN’(6.1μg/g FW)and ’ON’(5.15μg/g FW).But total carotenoid content in pulp of ’ON’(6.98 μg/g FW)was 11.4 fold of ’GN’(0.64 μg/g FW).Chromoplasts were observed only in pulp of ’ON’.2.Analysis of relative expression of carotenogenic genes in banana fruitsIn peel of ’GN’ and ’ON’,fold change of relative expression of carotenogenic genes were less than four.Expression of carotenogenic genes showed no bias between ’GN’ and ’ON’.Relative expression of carotenogenic genes showed a higher increase in pulp of ’GN’ than ’ON’.It is worth noting that Psy2 b showed a 100 fold increase of relative expression during fruit development.High expression of carotenogenic genes is associated with high carotenoid content.So Psy2 b could be a potential gene for molecular breeding.High expression level of Psy2 b in ’ON’ was mainly transcripted from A genome.Sequence similarity of Psy2 b from A genome in ’GN’ and ’ON’ was 100%.3.Proteome analysis of banana fruit plup5355 and 5949 proteins were detected form ’GN’ and ’ON’ respectively.656 and 1250 proteins were unique in ’GN’ or ’ON’ saperately.In each variety,protein numbers have little difference among different development stages.Proteins which had higher fold change than 5% threshold at last development stage of ’GN’ and ’ON’ were mainly enriched in starch and sucrose pathway,pyruvate biosynthesis pathway and Glycolysis pathway.These protein profile may results in accumulation of 3-phosphate glycerate and pyruvate which are the precursor of carotenoid biosynthesis.14 proteins correlated with carotenoid metabolism were identified.DXR、GGPS、PDS and ZDS were found in all devoloping stage in both varieties.Their protein abundance are higher in ’ON’ than in ’GN’.In conclusion,the results of this research indicate that high transcription level of carotenogenic genes together with the strong source of carotenoid metabolism boost the biosynthesis of carotenoid,resulting in high level accumulation of carotenoid in banana fruit.