Cysteine Protease Inhibitors Reduce Enzymatic Browning of Potato by Lowering the Accumulation of Free Amino Acids.

Enzymatic browning is a major issue affecting the quality of processed potato (Solanum tuberosum L.). To understand the molecular mechanism of browning, transcriptional analyses were performed by employing potatoes that differed in browning. Coexpression analysis indicated that 9 out of 15 upregulated genes in browning-less groups encoded for potato protease inhibitors (StPIs). In addition, gene otology analysis showed that the enriched terms were mainly involved in protease inhibitors. Overexpression of cysteine StPI 143 and StPI 146 individually reduced browning and lowered protease activities and tyrosine and total free amino acid (FAA) contents, but they could not decrease polyphenol oxidase activity. Moreover, supplementing exogenous tyrosine or total FAAs into transgenic potato mash to wild-type amounts promoted mash browning, browning with total FAAs, more than with tyrosine, resembling wild-type levels. These results implied that cysteine StPIs reduced browning via lowering the accumulation of FAAs in addition to tyrosine. Our findings have enriched the knowledge about the roles and mechanisms of protease inhibitors in regulating enzymatic browning of potato, which provide new ways for controlling potato browning.

Rosa hybrida RhERF1 and RhERF4 mediate ethylene- and auxin-regulated petal abscission by influencing pectin degradation.

The timing of plant organ abscission is modulated by the balance of two hormones, ethylene and auxin, while the mechanism of organ shedding depends on the loss of middle lamella pectin in the abscission zone (AZ). However, the mechanisms involved in sensing the balance of auxin and ethylene and that affect pectin degradation during abscission are not well understood. In this study, we identified two members of the APETALA2/ethylene-responsive factor (AP2/ERF) transcription factor family in rose (Rosa hybrida), RhERF1 and RhERF4 which play a role in petal abscission. The expression of RhERF1 and RhERF4 was influenced by ethylene and auxin, respectively. Reduced expression of RhERF1 or RhERF4 was observed to accelerate petal abscission. Global expression analysis and real-time PCR assays revealed that RhERF1 and RhERF4 modulate the expression of genes encoding pectin-metabolizing enzymes. A reduction in the abundance of pectin epitopes was detected in the AZs of RhERF1 and RhERF4-silenced plants by immunofluorescence microscopy analysis. In addition, RhERF1 and RhERF4 were shown to bind to the promoter of the pectin-metabolizing gene ß-GALACTOSIDASE 1 (RhBGLA1), and reduced expression of RhBGLA1 delayed petal abscission. We conclude that during petal abscission, RhERF1 and RhERF4 integrate and coordinate ethylene and auxin signals to modulate pectin metabolism, in part by regulating the expression of RhBGLA1.

Effects of postharvest curing treatment on flesh colour and phenolic metabolism in fresh-cut potato products.

The flesh colour and phenolic metabolism in potato tuber during curing and after cut were investigated. Result indicated that postharvest curing not only changed phenolic metabolism during curing, but also improved fresh-cut colour for 12 days after fresh cut. Significantly lower PAL and higher phenolic content and PPO activities during curing treatment and fresh-cut potatoes were detected compared to the control, which lead to the lower browning in the slices from curing treated potatoes. HPLC analysis revealed that amounts of total phenolics, chlorogenic acid, gallic acid and protocatechuic acid were induced by curing and highly accumulated in the curing treated potatoes. Our results demonstrated that phenolic metabolism played an important role in the control of browning of fresh cut potato after curing.

Genes associated with opening and senescence of Mirabilis jalapa flowers.

A modest ethylene climacteric accompanies flower senescence in Mirabilis jalapa L., and exogenous ethylene accelerates the process. However, inhibitors of ethylene action and synthesis have little effect on the life-span of these ephemeral flowers. Treatment with alpha-amanitin, an inhibitor of DNA-dependent RNA synthesis, substantially delays the onset of senescence. This effect falls linearly between 7 h and 8 h after the start of flower opening. Subtractive hybridization was used to isolate transcripts that were up- and down-regulated during this critical period. Eighty-two up-regulated and 65 down-regulated transcripts were isolated. The genes identified encode homologues of a range of transcription factors, and of proteins involved in protein turnover and degradation. Real-time quantitative RT-PCR was used to examine expression patterns of these genes during flower opening and senescence. Genes that were identified as being down-regulated during senescence showed a common pattern of very high expression during floral opening. These genes included a homologue of CCA1, a 'clock' gene identified in Arabidopsis thaliana and an aspartyl protease. Up-regulated genes commonly showed a pattern of increase during the critical period (4-9 h after opening), and some showed very strong up-regulation. For example, the abundance of transcripts encoding a RING zinc finger protein increased >40 000 fold during the critical period.

Chalcone synthase as a reporter in virus-induced gene silencing studies of flower senescence.

Agrobacterium-mediated infection of petunia (Petunia hybrida) plants with tobacco rattle virus (TRV) bearing fragments of Petunia genes resulted in systemic infection and virus-induced gene silencing (VIGS) of the homologous host genes. Infection with TRV containing a phytoene desaturase (PDS) fragment resulted in reduced abundance of PDS transcripts and typical photobleaching of photosynthetic tissues. Infection with TRV containing a chalcone synthase (CHS) fragment resulted in silencing of anthocyanin production in infected flowers. The silencing phenotype ranged from scattered white spots on the normal purple background to entirely white flowers. Symptoms in the V26 cultivar were a diffuse mosaic, but infection of some purple-flowered commercial cultivars resulted in large white sectors and even entirely white flowers. Abundance of CHS transcripts in the white flowers was less than 4% of that in purple flowers on the same plant. Infection with TRV containing a tandem construct of PDS and CHS resulted in leaf photobleaching and white patterns on the flowers. Transcripts of CHS and PDS were reduced both in leaves and in flowers confirming simultaneous silencing of both genes by the tandem construct. We tested the effects of infection with TRV containing CHS and a fragment of a petunia gene encoding for 1-aminocyclopropane-1-carboxylate oxidase (ACO4) Abundance of transcripts encoding ACO4 and ACO1 were reduced (by 5% and 20%, respectively) in infected flowers. Whether the flowers were treated with ACC or pollinated, the white (silenced) flowers or flower sectors produced less ethylene and senesced later than purple (non-silenced) tissues. These results indicate the value of VIGS with tandem constructs containing CHS as reporter and a target gene as a tool for examining the function of floral-associated genes.