Unravelling the bruising discoloration of Agaricus bisporus, the button mushroom

In this research the browning-discoloration caused by bruising of button mushrooms was analysed. Brown-discoloration of mushrooms can amongst others be caused by the picking and storage of mushrooms. Current day commercial hybrids can not be used for mechanical harvesting because mushrooms are sensitive for discoloration. Mechanical harvesting can be used to lower the production costs of mushrooms. To make this possible new hybrids should be available that have a higher tolerance for bruising-discoloration. To breed for new hybrids the cause of bruising-discoloration needs to be analysed. This was done by analysing the compounds (substrates) involved in brown-discoloration and to look at the genes involved. These genes code for the enzymes involved in the conversion of the substrates into the dark brown pigment melanin. The research was performed with commercial and wild strains and the offspring of a segregating population. </p

Shortening of membrane lipid acyl chains compensates for phosphatidylcholine deficiency in choline-auxotroph yeast

Phosphatidylcholine (PC) is an abundant membrane lipid component in most eukaryotes, including yeast, and has been assigned multiple functions in addition to acting as building block of the lipid bilayer. Here, by isolating S. cerevisiae suppressor mutants that exhibit robust growth in the absence of PC, we show that PC essentiality is subject to cellular evolvability in yeast. The requirement for PC is suppressed by monosomy of chromosome XV or by a point mutation in the ACC1 gene encoding acetyl-CoA carboxylase. Although these two genetic adaptations rewire lipid biosynthesis in different ways, both decrease Acc1 activity, thereby reducing average acyl chain length. Consistently, soraphen A, a specific inhibitor of Acc1, rescues a yeast mutant with deficient PC synthesis. In the aneuploid suppressor, feedback inhibition of Acc1 through acyl-CoA produced by fatty acid synthase (FAS) results from upregulation of lipid synthesis. The results show that budding yeast regulates acyl chain length by fine-tuning the activities of Acc1 and FAS and indicate that PC evolved by benefitting the maintenance of membrane fluidity

Melanin biosynthesis pathway in Agaricus bisporus mushrooms

With the full genome sequence of Agaricus bisporus available, it was possible to investigate the genes involved in the melanin biosynthesis pathway of button mushrooms. Based on different BLAST and alignments, genes were identified in the genome which are postulated to be involved in this pathway. Seven housekeeping genes were tested of which 18S rRNA was the only housekeeping gene that was stably expressed in various tissues of different developmental stages. Gene expression was determined for most gene homologs (26 genes) involved in the melanin pathway. Of the analysed genes, those encoding polyphenol oxidase (PPO), the PPO co-factor L-chain (unique for Agaricus bisporus), and a putative transcription factor (photoregulator B) were among the highest expressed in skin tissue. An in depth look was taken at the clustering of several PPO genes and the PPO co-factor gene on chromosome 5, which showed that almost 25% of the protein encoding genes in this cluster have a conserved NACHT and WD40 domain or a P-loop nucleoside triphosphate hydrolase. This article will be the start for an in depth study of the melanin pathway and the role in quality losses of this economically important product

Main Phenolic Compounds of the Melanin Biosynthesis Pathway in Bruising-Tolerant and Bruising-Sensitive Button Mushroom (Agaricus bisporus) Strains

Browning is one of the most common postharvest changes in button mushrooms, which often results in economic losses. Phenolic compounds, which are associated with browning, were extracted from the nonbruised and bruised skin tissue of various button mushrooms with a sulfite-containing solution and analyzed with UHPLC-PDA-MS. In total, 34 phenolic compounds were detected. Only small differences in the total phenolic content between bruising-tolerant and -sensitive strains were observed. The contents of ¿-l-glutaminyl-4-hydroxybenzene (GHB) and ¿-l-glutaminyl-3,4-dihydroxybenzene (GDHB) correlated with bruising sensitivity; for example, R2 values of 0.85 and 0.98 were found for nonbruised brown strains, respectively. In nonbruised skin tissue of the strains with brown caps, the GHB and GDHB contents in sensitive strains were on average 20 and 15 times higher, respectively, than in tolerant strains. GHB and GDHB likely participate in the formation of brown GHB–melanin, which seemed to be the predominant pathway in bruising-related discoloration of button mushrooms

Main Phenolic Compounds of the Melanin Biosynthesis Pathway in Bruising-Tolerant and Bruising-Sensitive Button Mushroom (Agaricus bisporus) Strains

Browning is one of the most common postharvest changes in button mushrooms, which often results in economic losses. Phenolic compounds, which are associated with browning, were extracted from the nonbruised and bruised skin tissue of various button mushrooms with a sulfite-containing solution and analyzed with UHPLC-PDA-MS. In total, 34 phenolic compounds were detected. Only small differences in the total phenolic content between bruising-tolerant and -sensitive strains were observed. The contents of ¿-l-glutaminyl-4-hydroxybenzene (GHB) and ¿-l-glutaminyl-3,4-dihydroxybenzene (GDHB) correlated with bruising sensitivity; for example, R2 values of 0.85 and 0.98 were found for nonbruised brown strains, respectively. In nonbruised skin tissue of the strains with brown caps, the GHB and GDHB contents in sensitive strains were on average 20 and 15 times higher, respectively, than in tolerant strains. GHB and GDHB likely participate in the formation of brown GHB–melanin, which seemed to be the predominant pathway in bruising-related discoloration of button mushrooms

Browning sensitivity of button mushrooms

To study the sensitivity of Agaricus bisporus mushrooms to bruising, a reproducible method was developed to apply mechanical damage to mushroom caps and quantify the subsequent discoloration. The newly developed bruising device can apply damage to the cap tissue of intact button mushrooms by a slip-shear sliding process in a fast and reproducible way. A protocol has been developed to obtain the most reliable and reproducible method to compare bruising sensitivity of different A. bisporus strains. The severity of the bruise is quantified with a computer image analysis system. Pictures of the bruised mushroom caps were taken under controlled lighting conditions and calibrated to a local reference. Image analysis software was developed to calculate the whiteness index (L-(3xb*), as defined by Hunter). This method of bruising and image based quantification was subsequently applied to a collection of wild, commercial and hybrid A. bisporus strains. A significant difference was found between bruising sensitive mushrooms and bruising tolerant mushrooms. A correlation was found between discoloration by the bruising device and discoloration caused by transportation of mushrooms on a conveyor belt. Less correlation was found between post-harvest discoloration of undamaged stored mushrooms and the bruising device. This indicates that discoloration caused by bruising or by storage of intact mushrooms might have different mechanisms

A new method to apply and quantify bruising sensitivity of button mushrooms

Mushrooms are prone to develop brown discolouration due to bruising caused by mechanical damage during harvest, which leads to reduced quality of the mushrooms. In order to study the mechanism behind discolouration and to breed for bruise-related browning resistant strains, a high throughput bruise application method and reliable quantification of browning sensitivity is essential. In this study a new bruising device was developed to bruise mushrooms in a fast and reproducible way. The bruising device can apply damage to the cap tissue of button mushrooms by a slip-shear sliding process. The severity of the bruise was quantified with a computer imaging system combined with a newly developed software programme. A protocol was developed to obtain the most reliable and reproducible method to compare browning sensitivity of different Agaricus bisporus strains. For this purpose, the extent of damage applied, time between harvest and bruising, developmental stage of the mushrooms and flushes were taken into account. The new method of bruising and image based quantification was subsequently applied to a collection of wild, commercial and hybrid A. bisporus strains and a distinction could be made between bruise-related browning sensitive mushrooms and tolerant mushroom

Shortening of membrane lipid acyl chains compensates for phosphatidylcholine deficiency in choline-auxotroph yeast

Phosphatidylcholine (PC) is an abundant membrane lipid component in most eukaryotes, including yeast, and has been assigned multiple functions in addition to acting as building block of the lipid bilayer. Here, by isolating S. cerevisiae suppressor mutants that exhibit robust growth in the absence of PC, we show that PC essentiality is subject to cellular evolvability in yeast. The requirement for PC is suppressed by monosomy of chromosome XV or by a point mutation in the ACC1 gene encoding acetyl-CoA carboxylase. Although these two genetic adaptations rewire lipid biosynthesis in different ways, both decrease Acc1 activity, thereby reducing average acyl chain length. Consistently, soraphen A, a specific inhibitor of Acc1, rescues a yeast mutant with deficient PC synthesis. In the aneuploid suppressor, feedback inhibition of Acc1 through acyl-CoA produced by fatty acid synthase (FAS) results from upregulation of lipid synthesis. The results show that budding yeast regulates acyl chain length by fine-tuning the activities of Acc1 and FAS and indicate that PC evolved by benefitting the maintenance of membrane fluidity