Expressão de genes e atividade enzimática da parede celular durante o desenvolvimento de melões não-climatéricos (Cucumis melo L.)

Abstract

The melon (Cucumis melo L.) is a crop of significant agricultural and economic importance. One of its most notable characteristics is its high genetic variability, presenting both climacteric and non-climacteric phenotypes, which directly influence fruit ripening. The ripening process of the melon affects its aroma, flavor, sugar concentration, color, and texture, the latter being related to the post-harvest texture and durability of the fruit due to the presence of the cell wall. The loss of firmness in non-climacteric fruits is associated with the regulation of gene expression that controls cell wall components. Thus, the aim of this study is to elucidate the expression pattern of the following genes: CmAGL1 (α-galactosidase), CmCEL (Endoglucanase), CmXGT (xyloglucan glycosyltransferase), CmXYL (β-D-xylosidase protein family), CmXTH1 and CmXTH2 (Xyloglucan endotransglucosylase/hydrolase), CmPGL1 and CmPGL2 (Polygalacturonases), CmPGN (Polygalacturonase-1 non-catalytic beta subunit), and CmEXP (Expansin-like A2) at the maturation stages of 15, 25, 35, and 45 days after pollination (D.A.P) in the cell wall metabolism of non-climacteric melon fruits cv. ‘Eldorado’, using reverse transcription followed by polymerase chain reaction (RT-qPCR).

The fruits were cultivated in a greenhouse and harvested at 15, 25, 35, and 45 D.A.P. Post- harvest analyses, primer design, total RNA extraction, conversion to cDNA, and RT-qPCR

analyses were conducted, and the data were subjected to variance analysis (ANOVA) and Tukey’s test at 5% significance. The primers for genes CmPGL1 and CmPGL2 were not suitable for RT-qPCR analyses. The genes CmAGL1, CmCEL, CmXYL, CmXTH1, CmXTH2, CmEXP, and CmPGN were more highly expressed at the early stages of maturation, especially at 25 days after pollination (D.A.P), during which the activity of cell wall component degradation enzymes occurs, resulting in increased fruit weight and firmness. The CmXGT gene was more highly expressed at 45 D.A.P. At 35 and 45 D.A.P, a decrease in fruit firmness was observed due to the solubilization of cellulose, hemicellulose, and pectin. The activity of polygalacturonase and β-D-xylosidase enzymes began at 25 D.A.P and remained high until full fruit maturation. Positive correlations were observed between the expression of CmAGL1 and CmPGN, CmAGL1 and CmXTH1, CmXTH1 and CmPGN, CmXTH1 and CmXTH2, as well as between the expression of CmEXP and the activity of polygalacturonases, and between the activity of β-D-xylosidases and the activity of polygalacturonases. Conversely, negative correlations were identified between the expression of CmCEL and CmXGT, between the expression of CmXGT and fruit firmness, and between the activity of β-D-xylosidases and firmness. It is concluded that the genes related to the cell wall are more highly expressed at 25 D.A.P and are associated with cell expansion, with their expression regulated by various factors.