Genomics of Papaya Fruit Development and Ripening

Abstract

Papaya (Carica papaya L.) is the first fleshy fruit with a climacteric ripening pattern to be sequenced. Many of the predicted papaya genes potentially involved in fruit growth, development, and ripening have homology to those involved in tomato fruit size and shape. Fewer genes that may impact sugar accumulation in papaya, ethylene synthesis and response, respiration, chlorophyll degradation, and carotenoid synthesis are predicted than in tomato. Similar or fewer genes were found in papaya for the enzymes leading to volatile production than so far determined for tomato. Similar numbers or fewer genes are found in papaya for the enzymes leading to volatile production than so far determined for tomato. The presence of fewer papaya genes in most fruit development and ripening categories suggests less subfunctionalization of gene action. The lack of whole genome duplication and reductions in most gene families and biosynthetic pathways make papaya a valuable and unique tool to study the convergent evolution of fruit ripening. The available data suggest that few phylogenetic constraints exist in the evolution of fruit type with fleshy fruits appearing independently in different plant families. The evolutionary origin and fundamental molecular mechanisms that lead to the development of the fruit ripening syndrome are unknown. Abscission-like cell separation processes that occur in leaves, petals, flowers, and pollen show parallel to fruit ripening in terms of physiology and biochemistry and potentially in the network and clusters of genes expressed. A global understanding of the evolution of the complex regulatory networks controlling the modules active during fruit ripening could lead to new regulatory controls that could limit postharvest losses in fruits.