Ethylene biosynthesis and perception during ripening of loquat fruit (Eriobotrya japonica Lindl.)

In order to gain insights into the controversial ripening behavior of loquat fruits, in the present study we have analyzed the expression of three genes related to ethylene biosynthesis (ACS1, ACO1 and ACO2), two ethylene receptors (ERS1a and ERS1b), one signal transduction component (CTR1) and one transcription factor (EIL1) in peel and pulp of loquat fruit during natural ripening and also in fruits treated with ethylene (10μLL^-1) and 1-MCP (10μLL^-1), an ethylene action inhibitor. In fruits attached to or detached from the tree, a slight increase in ethylene production was detected at the yellow stage, but the respiration rate declined progressively during ripening. Accumulation of transcripts of ethylene biosynthetic genes did not correlate with changes in ethylene production, since the maximum accumulation of ACS1 and ACO1 mRNA was detected in fully coloured fruits. Expression of ethylene receptor and signaling genes followed a different pattern in peel and pulp tissues. After fruit detachment and incubation at 20°C for up to 6days, ACS1 mRNA slightly increased, ACO1 experienced a substantial increment and ACO2 declined. In the peel, these changes were advanced by exogenous ethylene and partially inhibited by 1-MCP. In the pulp, 1-MCP repressed most of the changes in the expression of biosynthetic genes, while ethylene had almost no effects. Expression of ethylene perception and signaling genes was barely affected by ethylene or 1-MCP. Collectively, a differential transcriptional regulation of ethylene biosynthetic genes operates in peel and pulp, and support the notion of non-climacteric ripening in loquat fruits. Ethylene action, however, appears to be required to sustain or maintain the expression of specific genes.