Abstract
The edible mushroom Volvariella volvacea is an important crop in Southeast Asia and is predominantly harvested in the egg stage. One of the main factors that negatively affect its yield and value is the rapid transition from the egg to the elongation stage, which has a decreased commodity value and shelf life. To improve our understanding of the changes during stipe development and the transition from egg to elongation stage in particular, we analyzed gene transcription in stipe tissue of V. volvacea using 3′-tag based digital expression profiling. Stipe development turned out to be fairly complex with high numbers of expressed genes, and regulation of stage differences is mediated mainly by changes in expression levels of genes, rather than on/off modulation. Most explicit is the strong up-regulation of cell division from button to egg, and the very strong down-regulation hereof from egg to elongation, that continues in the maturation stage. Button and egg share cell division as means of growth, followed by a major developmental shift towards rapid stipe elongation based on cell extension as demonstrated by inactivation of cell division throughout elongation and maturation. Examination of regulatory genes up-regulated from egg to elongation identified three potential high upstream regulators for this switch. The new insights in stipe dynamics, together with a series of new target genes, will provide a sound base for further studies on the developmental mechanisms of mushroom stipes and the switch from egg to elongation in V. volvacea in particular.
Highlights
The edible straw mushroom Volvariella volvacea is popular in the diets of Southeast Asia and ranks high (5th) in terms of annual world-wide production [1,2,3]
Studies on exg2 of the mushroom Lentinula edodes identified a glycoside hydrolase family 55 (GH55) exo-b-1,3-glucanase with a function in stipe elongation [25,26] and we recently reported possible involvement of exg2 in stipe elongation in V. volvacea [27]
Analysis of differentially expressed genes (DEGs) between successive stipe stages To increase the resolution of functional transitions during stipe development, we focused on expression level changes of genes between successive stages: BU to EG, EG to EL and EL to MA (Figure 1, 2, Table S6)
Summary
The edible straw mushroom Volvariella volvacea is popular in the diets of Southeast Asia and ranks high (5th) in terms of annual world-wide production [1,2,3]. V. volvacea is harvested in its egg stage, since taste, shelf life, nutritious and commodity value are considerably better in this than in later developmental stages [4]. Egg stage fruiting bodies are characterized by a pileus and stipe that are still fully enclosed by the universal veil (exopellicle) causing an egg shaped appearance (Figure 1A). Rapid stipe extension to near full length in the elongation stage ruptures the exo-pellicle (forming the volva) on average in 5–12 hours, periods of as little as 3 hours are possible. The elongation stage quickly advances to the maturation stage, with extension of the stipe to its final length, unfolding of the pileus, and lastly sporulation and deterioration
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