For those less familiar with the Apprenticeship, it is a six month, full-time organic training for up to 38 apprentices from around the world. The roots of the program extend to the arrival of Alan Chadwick at UCSC 40 years ago, when he and a group of student “apprentices” created the Student Garden Project . Apprentices have traditionally been allowed to live on the farm in their own tents for the six months, sharing cooking and other chores in the Farm Center kitchen and dining room. As a past apprentice and staff member, Boyce-Abel said that for her the planned apprentice housing demonstrated a new level of support from UCSC and a new, more permanent status for the Apprenticeship. When the campus approved the apprentice housing project, Garden Manager Orin Martin said, “This represents staying power.” The apprentice tent cabins, planned as “light-on-the-land,” appropriate technology structures tucked in behind the plum orchard, will give the program a solid foundation. Olivia’s challenge inspired a $20,000 gift from 1978-79 apprentice Meg Cadoux Hirshberg and her husband Gary Hirshberg , whose gift amount allows them to name one of the cabins. Phyllis Anderson, a 1967-70 apprentice and a Friends member, large square planting pots pledged $5,000 which entitles her to name one room of a cabin, as will Jeannine Bonstelle Bassett’s $5,000 gift through the Silent Gong Fund.
Many other apprenticeship graduates and Friends of the Farm & Garden members have also supported the project with gifts and pledges. With these gifts, added to the Center facilities funds set aside for this purpose and funds brought in through this summer’s Back 40 event, more than half the needed $487,000 has been raised. Should you be inspired to donate now, please send a check to the above address made out to the UCSC Foundation with “Apprentice Housing Project” in the memo line.To subsist as an herbivore, an organism must overcome substantial barriers in the form of physical or chemical plant defenses and less than optimal nutrient availability. In some instances, the plant defenses interact directly with nutrient availability by decreasing uptake or impeding digestion , although myriad mechanisms have been described for how herbivores adapt to or avoid defenses. In addition to these deterrents, plant tissues typically maintain high carbon to nitrogen ratios, and plant fluids are depleted in many essential amino acids, making it more difficult for herbivores to acquire nitrogen-based nutrients. To overcome these dietary limitations, herbivores evolved partnerships with bacteria that facilitated transitions to new feeding niches, e.g., on phloem or xylem, or otherwise augmented plant palatability by attenuating defenses. Symbioses can fail, however, when symbiont genomes degrade or limit host range . Thus, there is likely selection pressure to either replace symbionts with more efficient ones, or to evolve novel feeding strategies to avoid symbiont dependence. Indeed, several hemipteran lineages, including leaf hoppers and the Phylloxeridae , have transitioned to novel plant-feeding strategies and lost their obligate symbiont associations.
The transitions in and out of symbioses have left genomic signatures such as reduced genome structure and function for many obligate symbionts, although the effects of symbiosis on herbivore genomes with or without symbionts is unknown.The metabolic coordination in amino acid synthesis and usage between bacteria and host requires amino acid transporters that function in transporting amino acids across the insect/symbiont interface, membranes that separate the cytoplasm of symbionts from insect hemolymph. Two types of AATs mediate this transport: the amino acid polyamine organocation transporter superfamily and the amino acid/auxin permease transporters family . Although both groups belong to the APC superfamily, members of the AAAP family have relatively divergent amino acid sequences, varying substrate specificities, and 11 transmembrane domains, compared to other transporters of the APC family. Expression profiles of these two families of AAT genes for several herbivorous species and their bacterial endosymbionts support a role for these transporters in the evolution of nutritional endosymbiosis. A growing body of evidence has demonstrated that insects induce nutrient sinks in plants in the form of galls that abundantly supply minerals, carbohydrates, and free amino acids. Given that numerous insect taxa form galls, an intriguing question arises: how does the accessibility of gall-enriched nutritive compounds influence the evolution of insect hosts and/or their symbionts? Among the Sternorrhyncha, few lineages secondarily lost endosymbionts concurrent with a shift to parenchyma feeding, and some taxa, such as the Phylloxeridae also induce galls. Insects within the Phylloxeridae are considered sister to the aphids and adelgids , groups that also retain galling and free-living species.
In contrast with aphids and adelgids that harbor symbionts in bacteriocytes, Phylloxeridae species lack stable intracellular symbionts. Further, Phylloxeridae comprises numerous life history strategies, including galling and free-living species that allow a phylogenetically controlled comparison to understand how these strategies arose with respect to their nutrient acquisition and metabolism. As an important grape pest worldwide, the grape phylloxera is capable of making leaf and root galls and its interaction with plant hosts has been the most investigated among the Phylloxeridae. Studies showed that infestation of D. vitifoliae reprograms plant metabolism, leading to the accumulation of nutrients such as carbohydrates and free amino acids. Recently, D. vitifoliae AATs were compared to paralogs in aphids to help pinpoint which transporters underlie the maintenance of nutrient symbiosis between aphids and Buchnera with an emerging conclusion that ecological context may contribute to AAT gene copy number and evolution. To expand the understanding of amino acid metabolism associated with herbivorous insects, we compared species that manipulate plant host amino acid content by gall forming to free-living species, and among species with and without stable nutritional endosymbionts. We sequenced the transcriptomes of nine Phylloxeridae species including D. vitifoliae and eight from the genus Phylloxera. Oak phylloxera has a free-living life history and thus was compared to other galling phylloxerid species regarding AAT evolution whereas two aphid species whose genomes are sequenced were compared to four other galling aphids. Our results indicated that galling insects, in Phylloxeridae and among aphidomorphs, experienced increased constraints on the evolution of AATs likely because of their ability to manipulate plant host metabolism.We collected nine known species within the Phylloxeridae for RNA sequencing. Phylloxeridae is a sister family of Adelgidae under the superfamily Phylloxeroidea, which is sister to the Aphidoidea: Aphididae all within the suborder Sternorrhyncha . These nine species include three that gall stems/petioles , one that feeds across hosts causing crinkles/folds in leaf veins , three that form spheres on leaves , one freely living , and one that galls both roots and leaves of Vitis species . In contrast to P. quercus that lives freely on oak trees , all the other Phylloxera species induce galls on different hickory species and/or tissues . Although the description of P. foveata places it on C. cordiformis and the individuals collected in this study came from C. glabra, we are considering the insects to be the same species for this study because of similarity in the induced phenotype. The Phylloxeridae represents an unresolved taxon , where ongoing research is delineating species. All Carya originating phylloxerids were collected from the Arnold Arboretum of Harvard University, Boston, Massachusetts. Phylloxera quercus was collected from Quercus sp. at a horticultural nursery in Bellevue, WA. Daktulosphaira vitifoliae was collected from native grapes near Madera Canyon, Arizona. Collected insect samples were stored in RNAlater solution at room temperature initially, transferred to 4 °C within eight hours for temporal storage , plastic square planter pots and later kept at −80 °C until RNA isolation. Insects at all stages were collected initially but separated to include only juveniles and adults for sequence analysis.Amino acid uptake, transport, and catabolism underlie the success of herbivory as a life history strategy. Here we present the first multigene tree for members within the Phylloxeridae; a family with both galling and free-living herbivores. We also present transcript profiles across fluid feeding herbivores that support plant host constraint on insect amino acid transporter evolution. Galling sap-feeding insects show fewer AAT transcripts than free-living species within the same insect families and within the same genus of Phylloxera. The ability of galling insects to manipulate plant nutrient content likely altered selection to retain or duplicate the number of functioning AATs within the insect.
Previous research suggests some AATs facilitate the evolution of endosymbioses but also that ecological context may interact with nutrient transporter evolution to shape adaptive duplication or loss. Our data advance this idea by highlighting how complex the selective environment is and suggest specialized interactions with plants play a large role in determining the evolution of herbivore genomes, especially when nutrient manipulating strategies are involved. Previous research on some AATs correlates gene expression and presence with the maintenance of endosymbioses; however, phylloxerids lack stable endosymbionts and still retain many of these same AATs. We found members of the Phylloxeridae family retain at least one copy of each APC found among other aphidomorphs with the exception of two clades that show duplications. Otherwise, phylloxerids retained at least one APC similar to many other Sternorrhyncha insects and D. melanogaster. Interestingly, free-living P. quercus often showed multiple AAT copies within clades where galling phylloxerids possessed only one copy . Free-living aphids also show a similar pattern compared to galling aphids for many clades . This increase within clades suggests that these paralogs may function generally to support nutrient transport when feeding on host parenchyma, atissue where nutrients are lower than when feeding on gall tissue where nutrients can be enriched by and for the galling insect. We hypothesize then that host nutrient manipulation altered the selection environment to maintain certain AATs. In support of this we identified fewer AATs in galling insects than free-living relatives. In some instances, galling phylloxerids did not accumulate specific AAT transcripts; however, lack of accumulation may result from a missing gene or lack of conditions under which expression occurs. While we recognize the limitations of transcriptome information to resolve this, the use of the D. vitifoliae and M. persicae genomes suggests all phylloxerid and nearly all aphid genes were accounted for, and that variation in AATs among genera occurs within aphidomorphs. Some Phylloxera species show accumulation of AATs absent from the D. vitifoliae genome whereas galling Phylloxera species show different numbers of AAT transcripts across clades. Similarly, some galling aphids also lack transcripts for some clades where free-living aphids retain one if not more transcripts. This provides support that differences in the nutrient environments across plant hosts differentially alter selection to retain certain AATs. Little information exists for comparing extensive metabolite profiles of hosts across galled taxa, but the diversity in morphology, color, and specialized tissues that are induced in plant hosts by galling insects suggests nutrient pools that insects feed upon differ widely. Future studies examining metabolite pools among closely related taxa will help resolve what limitations, if any, are present in induced plant phenotypes, and provide additional tests of the role of host nutrient manipulation in the evolution of insect AATs. The microbial community plays a fundamental role in animal nutrient acquisition from food, especially for sapfeeding insects where coevolution with endosymbiotic bacteria alleviates low amino acid content provided by phloem diets. Galling or less apparent manipulation of host nutrients increases nutrient flux to feeding sites, potentially altering selection on the stability of endosymbiotic relationships. Our data and previous transcriptome profiles support increases in paralogs for two free-living aphids, but no galling aphids share these increases. This pattern suggests lineage specificity; however, until more insects are profiled in a way that controls for phylogeny while spanning the range of plant nutrient manipulation, either host manipulation, lineage specific evolution, or both may alter selection on AAT gene evolution. Prior transcriptome assessments correlated transcript abundance and presence with maintaining endosymbiosis. By examining more phylloxerids, we increased resolution of slimfast gene evolution, providing support for previous data that all aphidomorphs experienced slimfast duplication . Thus, slimfast expansions likely occurred in the ancestral aphidomorph. Because the ancestral state of phylloxerids is unresolved without a phylogeny, it is possible that the ancestor lost AATs with the evolution of galling or gained AATs with the transition away from galling. Either scenario would link this clade to nutrient acquisition strategies. Although phylloxerids lack stable nutritional endosymbionts, numerous microbial partners exist within the gut microbiome .