S01 - Session O7 - Morphological and molecular characterization of fibrousness in mango fruit mesocarp

Authors: Mazal Ish shalom, Adi Doron-Faigenboim , Shay Tsaidi, Hanita Zemach, Amir Sherman, Yuval Cohen *

Mango ( Mangifera indica L.) is one of the most important fruit trees in tropical and subtropical regions. The fruit is a drupe with a fleshy edible mesocarp. The seed is covered with a hard fibrous endocarp, with the fibers penetrating from the endocarp into the mesocarp. Fibers characterize all mango cultivars, but some are considered more fibrous than others. High quality cultivars have short and soft fibers, but in fibrous cultivars, they are harder and may fill the entire mesocarp, hence negatively influencing customers' satisfaction. The aim of this study was the characterization of fiber formation in fibrous and non-fibrous accessions by characterizing fiber formation morphologically and histologically during fruit development and seed hardening of mango fruits of the different types. Fibers develop in the mesocarp at early stages, with hardening of the endocarps occurrig in all cultivars during development. During seed coat hardening, the fibers in the mesocarp, concomitant with those of the endocarp, are hardened, as detected by phloroglucinol-HCl staining, which detects lignin, of whole fruits. Fibers in the mesocarp of fibrous cultivars have larger cross section areas relative to those of non-fibrous cultivars. Next-generation sequencing performed on the mesocarp and endocarp tissues during seed hardening of four mango accessions revealed selective differential gene expression: Expression of various genes from the phenylpropanoid metabolic and biosynthetic pathway as well as genes involved in the secondary cell wall and lignin biosynthesis increased in both tissues in all accessions. Additionally, the level of specific genes in these processes increased in the mesocarp of fibrous cultivars. Our work sheds light on the differences between fibrous and non-fibrous cultivars, enabling a better understanding of the processes leading to fiber formation in the mesocarp. This information is valuable for developing markers for breeding of non-fibrous cultivars and for future biotechnological approaches to generate fibre-free cultivars.