Abstract
We investigated the fruit development in two plantain banana cultivars from two weeks after bunch emergence till twelve weeks through high-throughput proteomics, major metabolite quantification and metabolic flux analyses. We give for the first time an insight at early stages of starch synthesis and breakdown. Starch and sugar synthesis and breakdown are processes that take place simultaneously. During the first eight to ten weeks the balance between synthesis and breakdown is clearly in favour of sugar breakdown and a net starch synthesis occurs. During this period, plantain fruit accumulates up to 48% of starch. The initiation of the ripening process is accompanied with a shift in balance towards net starch breakdown. The key enzymes related to this are phosphoglucan water dikinase (PWD), phosphoglucan phosphatase, α-1,6-glucosidase starch debranching enzyme (DBE), alpha glucan phosphorylase (PHS) and 4-alpha glucanotransferase disproportioning enzyme (DPE). The highest correlations with sucrose have been observed for PHS and DPE. There is also a significant correlation between the enzymes involved in ethylene biosynthesis, starch breakdown, pulp softening and ascorbate biosynthesis. The faster ending of maturation and starting of ripening in the Agbagba cultivar are linked to the key enzymes 1-aminocyclopropane-1-carboxylate oxidase and DPE. This knowledge of the mechanisms that regulate starch and sugar metabolisms during maturation and ripening is fundamental to determine the harvest moment, reduce postharvest losses and improve final product quality of breeding programs.
Footnotes
S.C.C. and R.S. conceived the original screening and research plans; S.C. and Y.G. supervised the experiments; N.C. performed the experiments using the proteomics methods and S.C and A.M. performed the experiments based on the metabolome methods; D.A. performed the field experiment; C.C. provided technical assistance; S.C.C, N.C, S.C, A.M analyzed the data; N.C, and S.C.C. wrote the article with contributions of all the authors; S.C.C. supervised and completed the writing. S.C.C. agrees to serve as the author responsible for contact and ensures communication.
We acknowledge USAID for the project AID-BFS-G-II-00002-11 Reviving the plantain breeding program at IITA – International Institute for Tropical Agriculture. The authors would furthermore like to thank all donors who supported this work through their contributions to the CGIAR Fund (http://www.cgiar.org/who-we-are/cgiar-fund/fund-donors-2/), and in particular to the CGIAR Research Program on Roots, Tubers and Bananas, and the PHENOME (French ANR-11-INBS-0012) project for funding. The metabolite analyses were performed on Bordeaux Metabolome facility.