The Plant Press

From The Plant Press, Vol. 24, No. 3, July 2021.

Abstracts from the speakers of the 18^th Smithsonian Botanical Symposium 

The 18^th Smithsonian Botanical Symposium, “Plant symbiosis: The good, the bad, and the complicated,” was held 13-14 May 2021. The invited speakers explored current research in the diversity of plant symbioses, examining the relationships plants have with insects, fungi, bacteria, and even other plants. Below are the abstracts from the papers that were presented by the invited speakers. 

Naomi Pierce
Harvard University
"Context dependent evolution of the African ant acacia, Vachellia drepanolobium, and its multitude of symbionts"

The Whistling Thorn Acacia, Vachellia drepanolobium, is a dominant tree on black cotton soils of East African savannas. In exchange for protection against enemies, these ant acacias secrete food rewards from extra-floral nectaries and provide housing in the form of swollen stipular thorns for at least four different species of ant inhabitants. Ant acacias are finely adapted to read the signals of their ant partners, and experiments show they can respond selectively to volatile compounds from different ant species. In addition, abiotic factors such as the stoichiometry of soil nutrients can exert profound effects on these associations. Along with the ants, the trees host a cornucopia of myrmecophiles and microbes, each of which contributes to shape the context-dependent evolution of this complex symbiosis. Fungi in particular may interact symbiotically with host trees to enhance growth, and ants likely play an underappreciated role in vectoring fungi and bacteria between trees.

Jay Bolin
Catawba College
"Hydnora from fungus to foul flower: the natural history of the strangest plants in the world"

The parasitic genus Hydnora undoubtedly include the strangest plants in the world. Ranging from the Cape of Good Hope to the Horn of Africa and across the Red Sea to the Arabian Desert, the parasitic plant genus Hydnora has astounded and amazed naturalists that are fortunate enough to observe it. However, few encounter this bizarre and furtive plant parasite, because it spends most of its life underground stealing water and nutrients from the roots of host plants. When Hydnora emerges from the soil, the grotesquely beautiful flowers defy expectation by looking and smelling of rotting meat, indicators of an incredible pollination story. Bolin, an authority on this twisted branch of life, describes the history, ecology, and evolution of this wonderful group of botanical oddities, recounting explorations and new species discoveries from the restricted diamond fields of Namibia to the margins of the Rub’ al Kali desert in the Sultanate of Oman.

Posy Busby
Oregon State University
"Assembly and function of the leaf microbiome"

Non-pathogenic microfungi live in and on the leaves of all land plants. Individual fungi within these cryptic communities can alter plant disease severity by antagonizing or facilitating pathogens, or by modulating plant defense. Yet how the leaf mycobiome as a whole alters the landscape of plant disease is poorly understood. In this talk, Busby describes her work in Populus trichocarpa, the black cottonwood of the Pacific Northwest USA, which seeks to elucidate leaf mycobiome assembly processes and the consequences of the leaf mycobiome for plant disease.

Leonora Bittleston
Boise State University
"Convergent interactions in carnivorous pitcher plant microcosms"

The ‘pitchers’ of carnivorous pitcher plants are exquisite examples of convergent evolution. In addition to attracting and digesting prey, they house communities of living organisms. Bittleston asks if these communities also converge in structure or function. Using samples from more than 330 field-collected pitchers of eight species of Southeast Asian Nepenthes and six species of North American Sarracenia, she demonstrates that the pitcher microcosms are strikingly similar. Compared to communities from surrounding habitats, pitcher communities house fewer species. While communities associated with the two genera contain different microbial organisms and arthropods, the species are predominantly from the same phylogenetic clades. Microbiomes from both genera are enriched in degradation pathways and have high abundances of key degradation enzymes. Moreover, in a manipulative field experiment, Nepenthes pitchers placed in a North American bog assembled Sarracenia-like communities.

Dong Wang
University of Massachusetts Amherst
"Indentured servitude: host control of intracellular bacteria in the nitrogen-fixing symbiosis"

The nitrogen-fixing symbiosis between legumes and rhizobia carries enormous economic and environmental values. A defining feature of this interaction is the intracellular association of the microsymbiont with its host cell. Wang’s research group is searching for the host determinants that allow the bacteria to enter the host cytoplasm, survive in a membrane-bound compartment, and transform into a nitrogen-fixing organelle. One critical insight from their on-going investigation is that the membrane interface between the bacteria and the host cytosol is an important site for signal and nutrient exchange. The host cell redirects its secretory pathway to deliver onto or across this membrane a variety of important molecules, where they interact with the bacteria directly or indirectly to determine the outcome of this interaction.

Manuela Dal Forno
Fort Worth Botanic Garden | Botanical Research Institute of Texas
"The lichen dilemma: unveiling diversity in multi-species symbioses"

Lichens are complex symbiotic units formed by a main fungal partner, a green algal and/or a cyanobacterial partner, along with a diverse community of microorganisms. They represent an important and diverse biological group present in most terrestrial ecosystems, and a main nutritional strategy in Fungi. Despite being classic examples of symbioses, lichens remain broadly unknown systems given its multifaceted interactions and controversial definitions. In this talk, Dal Forno discusses current concepts in lichenology and utilizes her research in the subtribe Dictyonemateae to present examples of how diversity of symbiotic fungi and bacteria can shape our understanding of lichens.

Acknowledgements 

The success of the Symposium was due to the significant time and efforts of the following people:

Organizers: 

• Amy Bolton
• Laurence J. Dorr 
• Gary Krupnick 
• Susan Pell 
• Eric Schuettpelz 
• Kenneth Wurdack 
• Elizabeth Zimmer 

Support: 

• Mary Ann Apicelli, Administrative Specialist in Botany 
• Danielle Duran, Executive Assistant to the Deputy Director
• Adriana Reynolds, Fund Manager for Botany 

Sponsors of the 18^th Smithsonian Botanical Symposium 

• Department of Botany, National Museum of Natural History 
• United States Botanic Garden