Our group has several broad research interests, including plant-microbe and plant-animal interactions, as well as protein trafficking in plant cells. Each of these broad interests are currently being pursued through several integrated projects revolving around nectaries and nectar.
Flowering plants attract mutualistic animals by offering a reward of nectar. Specifically, floral nectar is produced to attract pollinators, whereas extrafloral nectar mediates indirect defenses (e.g. ant-plant interactions). There is a strong correlation between nectar quality (i.e. volume and composition) and the efficiency of the resulting plant-animal mutualism. Significantly, there is also a clear relationship between nectary form (the glands that produce nectar) and nectar quality. Remarkably, the molecular events involved in the development of nectaries, as well as the synthesis and secretion of the nectar itself, are poorly understood. Indeed, only a few genes have been reported to directly affect the de novo production or quality of floral nectar.
Comparative genomics of nectaries and nectar
According to our recent findings, the central components of active nectar secretion might be conserved across species and nectary type (floral vs. extrafloral). We hypothesize that nectar synthesis and secretion follows a central mechanism that is conserved among the core eudicots and applies to both floral and extrafloral nectar, and that this mechanism can be differentially regulated in different types of tissues, or species, in order to meet the physiological and ecological needs of the respective species. To test this hypothesis,the long-term goal of our group is to elucidate the genetic and physiological mechanisms that underlie nectary maturation and active nectar secretion, and to study the impact of select nectar components on specific plant-animal and plant-microbe interactions. In order to elucidate the conserved elements of these mechanisms we are applying a broad, comparative approach to the study of floral and extrafloral nectar/ies in a core group of dicotyledonous species.
Determining the molecular basis of nectar production can have broad implications, ranging from understanding the co-evolution of plant-animal interactions to increasing yields in multiple crop species, as well as targeted improvements in apiculture. For example, nearly 90% of flowering plant species produce nectar as a means to attract pollinators, including one-third of all crop species. U.S. pollinator-dependent crops have an estimated annual value of $25 billion.
Development of cultivars with increased nectar production
In a separate project we are developing crop plants with high levels of floral nectar production. An increase in nectar production results in a concomitant increase in pollinator visitation, pollination efficiency, and yield, even for highly selfing plant species. For example, pennycress is an emerging winter cover and seed crop and is one of the first cultivated plants to flower in Minnesota (mid-April to early May). Our hypothesis is that cultivated pennycress may serve as an important source of nutrition for honeybees and other pollinators in the spring when other plants are not yet flowering at an appreciable level in Minnesota. In particular, the development pennycress plants with enhanced nectar production would provide an important ecosystem service. Pollinator nutrition has become an area of intense research as a means to stem declining pollinator numbers, particularly for honey bees. Cultivars with stably enhanced levels of nectar production are now being developed and will be evaluated for their ability to impact pollinator visitation and yield.
Solhaug EM, Johnson E, Carter CJ (2019) Metabolic profiling of Cucurbita pepo nectaries provides insights into carbon allocation and sugar signaling during nectar secretion. Plant Physiology. 180: 1930–1946.
Solhaug EM, Roy R, Chatt EC, Klinkenberg PM, Mohd-Fadzil N-A, Hampton M, Nikolau BJ, Carter CJ (2019) An integrated transcriptomics and metabolomics analysis of the Cucurbita pepo nectary implicates key modules of primary metabolism involved in nectar synthesis and secretion. Plant Direct, DOI: 10.1002/pld3.120.
Prasifka JR, Mallinger RE, Portlas ZM, Hulke BS, Fugate KK, Paradis T, Hampton ME, Carter CJ (2018) Using nectar-related traits to enhance crop-pollinator interactions. Frontiers in Plant Science, 9: 812.
Schmitt AJ, Sathoff AE, Holl C, Bauer B, Samac DA, Carter CJ (2018) The major nectar protein of Brassica rapa is a non-specific lipid transfer protein with strong antifungal activity. Journal of Experimental Botany. 69: 5587-5597.
Schmitt AJ, Roy R, Klinkenberg PM, Jia M, Carter CJ (2018) The octadecanoid pathway, but not COI1, is required for nectar secretion in Arabidopsis thaliana. Frontiers in Plant Science, 9: 1060.
Chatt EC, von Aderkas P, Carter CJ, Smith D, Elliott M, Nikolau BJ (2018) Sex-dependent variation of pumpkin (Cucurbita maxima cv Big Max) nectar and nectaries as determined by proteomics and metabolomics. Frontiers in Plant Science. 9: 860.
Thomas JB, Hampton MW, Dorn KM, Marks MD, Carter CJ (2017) The pennycress (Thlaspi arvense L.) nectary: structural and transcriptomic characterization. BMC Plant Biology, 17: 201.
Roy R, Schmitt A, Thomas J, Carter CJ (2017) Nectar biology: From molecules to ecosystems, Plant Science, 262: 148-164.
Olson AO, Carter CJ (2016) The involvement of hybrid cluster protein 4, HCP4, in anaerobic metabolism in Chlamydomonas reinhardtii. PLoS ONE, 11(3): e0149816.
Wiesen LB, Bender RL*, Paradis T, Larson A*, Perera MADN, Nikolau BJ, Olszewski NE, Carter CJ (2015) A role for GIBBERELLIN 2-OXIDASE6 and gibberellins in regulating nectar production. Molecular Plant, 9: 753–756
Lin I, Chen L-Q, Sosso D, Gase K, Kim S-G, Kessler D, Klinkenberg PM, Gorder MK, Qu X-Q, Hou B- H, Carter CJ, Baldwin IT, Frommer WB. (2014) Nectar secretion requires sucrose phosphate synthases and the sugar transporter SWEET9, Nature, 508: 546-549.
Bender RL, Fekete ML, Klinkenberg PM, Hampton MW, Bauer B, Malecha M, Lindgren K, Maki J, Perera MADN, Nikolau BJ, Carter CJ (2013) PIN6 is required for nectary auxin response and short stamen development, Plant Journal, 74: 893-904.
Bender R*, Klinkenberg P, Jiang Z, Bauer B*, Karypis G, Nguyen N, Perera MADN, Nikolau BJ, Carter CJ (2012) Functional genomics of nectar production in the Brassicaceae. FLORA, 7: 491-496.
Xu WW, Carter C (2010) Parallel multiplicity and error discovery rate (EDR) in microarray experiments. BMC Bioinformatics, 11: 465.
Agee AE, Surpin M, Sohn EJ, Girke T, Rey AR, Kram BW, Carter C, Wentzell AM, Kliebenstein DJ, Jin HC, Park OK, Jin H, Hicks GR, Raikhel N (2010) MODIFIED VACUOLE PHENOTYPE1 is an Arabidopsis myrosinase-associated protein involved in endomembrane protein trafficking. Plant Physiology, 152: 120-132.
Ruhlmann JM, Kram BW, Carter CJ (2010) CELL WALL INVERTASE 4 is required for nectar production in Arabidopsis. Journal of Experimental Botany, 61: 395-404.
Kram BW, Xu WW, Carter CJ (2009) Uncovering the Arabidopsis thaliana nectary transcriptome: investigation of differential gene expression in floral nectariferous tissues. BMC Plant Biology 9: 92.
Kram, BW, Bainbridge EA, Perera MADN, Carter C (2008) Identification, cloning and characterization of a GDSL lipase secreted into the nectar of Jacaranda mimosifolia. Plant Molecular Biology 68: 173-183.