Bridgewater Review

Volume 4 | Issue 1 Article 15

Apr-1986 Research Note: Do Mushrooms Have a Sex Life? Diane Cope Peabody Bridgewater State College

Robert B. Peabody

Recommended Citation Peabody, Diane Cope and Peabody, Robert B. (1986). Research Note: Do Mushrooms Have a Sex Life?. Bridgewater Review, 4(1), 26-27. Available at: http://vc.bridgew.edu/br_rev/vol4/iss1/15

This item is available as part of Virtual Commons, the open-access institutional repository of Bridgewater State University, Bridgewater, Massachusetts. Research Note Do Mushrooms Have A Sex Life?

Figure 1. Cluster of Armillaria mellea Diane Cope Peabody Robert B. Peabody

hen people learn of our research on eastern United States at the bases ofdead or appearance but also in their nutritional W mushrooms, they usually assume dying trees and tree stumps. Severe infesta­ relationships with plants. that we cook our subjects after we have tions occur west of the Rocky Mountains, When studying the life cycles of mush­ dissected them. In fact, the honey mush­ especially in California, where they cause rooms, it becomes apparent that, in gen­ room, the particular variety we study, is root rot of fruit and nut crops, ornamental eral, the mushroom's reproductive cycle is highly edible, and each fall, during the brief trees and shrubs. To date, over 600 species surprisingly similar to our own. Like hu­ period when the familiar mushrooms ap­ of plants have been reported to be suscepti­ man beings, mushrooms reproduce sex­ pear, collectors harvest baskets of the ble to attack by this fungus. In addition to ually: they form sex cells which, like the prized fungi from stumps or from the bases parasitic attacks on living plants and sap­ human sperm and egg cells, have half the of old trees. Nevertheless, the only mush­ rophytic growth on dead or dying trees, the number of chromosomes found in other rooms we have eaten have been supplied by honey mushroom is sometimes involved in body cells and are therefore referred to as grocery stores or restaurants. Having stud­ mutually beneficial relationships with sev­ "haploid." These sex cells eventually fuse ied the honey mushroom for over twelve eral species of trees and with at least two to produce somatic cells (cells other than years, we feel that it would be a little like species of orchids. Honey mushrooms, reproductive cells) with double the number eating an old friend. therefore, show a diversity not only in of chromosomes and are called "diploid." Species of the honey mushroom (Armil­ The idea that such simple organisms as laria mellea spp.) live throughout temperate mushrooms have the same kind of repro­ regions of the world. Their name reflects ductive process as human beings seems the fact that many are honey colored. quite remarkable. However, the group as a whole ranges in Although mushrooms definitely do have color from bright yellow to dull brown, a sex life, not all ofthe details ofthat sex life usually having minute scaly outgrowths on are understood in all species. (Mushrooms the cap and when young, a collar around are notably secretive about these matters.) the stalk. We were interested in studying the honey Reportedly good to eat, the honey mush­ mushroom in particular to learn exactly rooms are also "eaters" themselves and do how.and when certain cells become haploid a great deal of damage in the proc.ess. In and others become diploid (fig. 3). We fact, horticulturists and forest pathologists know that the honey mushroom produces on six continents are very much interested four kinds of spores (sex cells) which in this mushroom because ofits devastating appear under its cap in fall. These spores effects on crops and both commercially drop to the ground and germinate; compati­ managed and natural forests. Clumps of ble pairs of germinated spores mate and these mushrooms are often seen in the Figure 2. Armillaria mellea form cells containing the diploid number of

26 chromosomes (cell type A). This part of the sexual cycle has been duplicated in the Diploid ? laboratory. Since compatible matings gen­ erally result in the formation of a mush­ room, we then wanted to find the exact location within the mushroom of diploid ··-1---..... cells and the specific manner in which the diploid cells give rise to haploid cells, such as those found in cell type B (fig. 3). 8 In order to do this, we carefully removed tissues from specific parts of freshly col­ t Cell type A with a lected honey mushrooms. We used a DNA­ I/ single diploid nucleus specific stain to find out whether the cells were haploid or diploid. (DNA is the hereditary material of which genes are primarily composed.) The DNA-specific 0 Haploid spore Haploid stain attaches only to the DNA and causes ~ DNA to fluoresce when it is illuminated through a microscope with particular wave­ Fertilization lengths of light. The amount of light emit­ ted by the fluorescing DNA is proportional to the amount of DNA present and can be quantified by a photometer attached to a microscope. A haploid cell, for example, emits only half the light that a diploid cell ':G:r- \- emits when subjected to excitation wave­ Sj lengths of light. Material for study was readily available Haploid cells prior to mating in the fall, as we have at that time a cluster of honey mushrooms in our backyard in Bridgewater. This is very convenient, as it Figure 3. Life cycle of Armillaria mellea made the collection of fresh samples at just the right stage of development a simple matter. As we began to quantify the DNA content of cells in close proximity to cell samples for study. We even enlisted the body ofindividual mushrooms. This varies type B, we were surprised to find that every help of family members living in Worces­ considerably from the situation in humans cell was haploid. Thinking that the source ter. Thirteen mycologists responded, in­ and most other diploid organisms where of diploid cells must be farther from cell cluding seven from New York, Pennsyl­ somatic cells have the same chromosomes. type B than we had thought at first, we vania, and Massachusetts whose samples We are attempting to test the genetic sampled cells from the cap and stalk of were fresh enough to study using our mosaic hypothesis by recovering individual individual mushrooms. To our surprise, we technique. Again we found that all samples cells from the stalk region of individual were still unable to find diploid cells. Our have mushrooms composed primarily of mushrooms and testing them for among­ current thinking is that diploid cells of haploid cells. It now appears that what cell genetic variation. If it turns out that "type A" must occur in one of the earlier looked like an unusual condition in our honey mushrooms are genetic mosaics of stages of the life cycle which is completed isolated form of the honey mushroom is several different cell types, this information below ground prior to formation of the the general rule in this group offungi rather may be useful in understanding their broad familiar "mushroom" stage above ground. than the exception. range ofcolors and host nutritional relation­ We have collected samples of various sub­ Although our finding is of interest pri­ ships. This, in turn, may provide insight terranean tissues ofhoney mushrooms and marily to a rather restricted group ofbiolo­ into determining a control for this devas­ are continuing to look for the diploid "type gists, the classical mycologists, it has an tating plant pathogen. A" cells. implication which is of interest to a much Although the fact that honey mush­ The haploid condition of cells in the broader group. Based on what is known rooms do have a sex life has long been honey mushrooms was unexpected based about the process of haploidization (dip­ known, many details of that sex life still on previous mycologists' (scientists who loid cells becoming haploid) in other organ­ remain mysterious. study fungi) reports. In order to determine isms, the presence of haploid cells in the whether our Bridgewater honey mushroom stalk and cap ofa mushroom suggests that a was an aberrant form or whether honey genetic mosaic may exist in these organ­ Diane Cope Peabody is a professor at Bridge­ mushrooms are composed of haploid cells isms. That is to say that cells with different water State College in the Department of Bio­ in general, we wrote to mycologists in the combinations of somatic chromosomes logical Sciences. Robert B. Peabody is a member northeastern United States and requested and genes may exist, side by side, within the of the Biology Department at Swnehill College.

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