Gene expression associated with chlorophyll degradation and color transformation in a spontaneous bud mutation of navel orange

Abstract

Color mutations on citrus skin are a common occurrence and can serve as indicators of fruit maturation in citrus. In this study, a new early maturing navel orange cultivar, Lei Zao 1 Hao (MT), was identified as a spontaneous bud mutation from the Leibo Navel Orange (WT). To assess the differences between these two cultivars, the coloration of the fruit, the sugar content, and the levels of acid were examined throughout the ripening process. The study findings revealed that over the course of the fruit's development, the external peel color progressively turned orange. MT exacerbated the decline in H° while increasing L*, a*, and b*, and the chlorophyll level of the MT peel was continuously lower than that of WT, which coincided with a decrease in chlorophylls a and b. Compared to WT, MT had higher expression levels of genes linked to chlorophyll degradation, including CitCLH, CitNYC1, CitPPH, CitPAO, CitCAB1, and CitCAB2. The elevated expression of these genes in MT may potentially be associated with the initial color transformation process. In addition, the MT accelerated the accumulation of TSS and total sugar, especially before the 189 DAF of ripening. In short, ‘Lei Zao 1 Hao’ is a new option of navel orange available with extremely early maturity and a higher sugar content.