Down-Regulation of PpBGAL10 and PpBGAL16 Delays Fruit Softening in Peach by Reducing Polygalacturonase and Pectin Methylesterase Activity

Abstract

β-galactosidases are cell wall hydrolases that play an important role in fruit softening. However, <i>PpBGAL</i>s mechanism impacting on ethylene-dependent peach fruit softening was still unclear. In this study, we found that <i>PpBGAL4, -6, -8, -10, -16</i>, and -<i>17</i> may be required for ethylene-dependent peach softening and <i>PpBGAL10</i>, -<i>16</i> may make a main contribution to it among 17 <i>PpBGALs</i>. Utilization of virus-induced gene silencing (VIGS) showed that fruits were firmer than those of the control at 4 and 6 days after harvest (DAH) when <i>PpBGAL10</i> and <i>PpBGAL16</i> expression was down-regulated. Suppression of <i>PpBGAL10</i> and <i>PpBGAL16</i> expression also reduced <i>PpPG21</i> and <i>PpPME3</i> transcription, and polygalacturonase (PG) and pectinmethylesterases (PME) activity. Overall, total cell wall material and protopectin slowly declined, water-soluble pectin slowly increased, and cellulose and hemicellulose was altered significantly at 4 DAH, relative to control fruit. In addition, <i>PpACO1</i> expression and ethylene production were also suppressed at 4 DAH because of inhibiting <i>PpBGAL10</i> and <i>PpBGAL16</i> expression. These results suggested that down-regulation of <i>PpBGAL10</i> and <i>PpBGAL16</i> expression delays peach fruit softening by decreasing PG and PME activity, which inhibits cell wall degradation and ethylene production.