CLONING AND EXPRESSION ANALYSIS OF TWO EXPANSIN GENES FROM LOQUAT FRUIT

Expansins are shown to contribute to fruit softening. To understand the relationship between firmness change patterns and gene expression in fruits of (Eriobotrya japonica), two cDNA expansin genes were identified from mature loquat fruit and their expression profiles were then examined in pulp at different storage stages, by application of ethylene and low temperature. Two cDNA fragments of 531 bps encoding expansin proteins, named as EjExp1 and EjExp2, respectively, were isolated from mature fruit using RT-PCR. Sequence comparison showed that the homology between the 2 expansin genes was 77.4% at nucleotide level and 84.2% at amino acid level, respectively. Northern blot analysis exhibited that mRNA accumulation of both EjExp1 and Ej-Exp2 could be detected in fruit stored at 20 and 6°C, with a stronger expression of EjExp1 than EjExp2. The accumulation of EjExp1 mRNA of fruit stored at 20°C increased at day 1 but almost disappeared at day 2 and again increased till the end of storage at day 8. Treatment with propylene could slightly increase accumulation of EjExp1 mRNA at 20°C. At 6°C, EjExp1 mRNA accumulation increased at the first 7 days, then decreased gradually at the second two weeks and finally remained almost constant, while the mRNA of EjExp2 of fruit stored 20 and 6°C showed low and almost constitutive expression patterns. Propylene treatment had no effect on the expression of EjExp1 and EjExp2. These results suggested that the mRNA accumulation profiles of both EjExp1 and EjExp2 may be related to changes in firmness patterns of harvested loquat fruit.