Induced responses contribute to rapid adaptation of Spirodela polyrhiza to herbivory by Lymnaea stagnalis.

Herbivory-induced responses in plants are typical examples of phenotypic plasticity, and their evolution is thought to be driven by herbivory. However, direct evidence of the role of induced responses in plant adaptive evolution to herbivores is scarce. Here, we experimentally evolve populations of an aquatic plant (Spirodela polyrhiza, giant duckweed) and its native herbivore (Lymnaea stagnalis, freshwater snail), testing whether herbivory drives rapid adaptive evolution in plant populations using a combination of bioassays, pool-sequencing, metabolite analyses, and amplicon metagenomics. We show that snail herbivory drove rapid phenotypic changes, increased herbivory resistance, and altered genotype frequencies in the plant populations. Additional bioassays suggest that evolutionary changes of induced responses contributed to the rapid increase of plant resistance to herbivory. This study provides direct evidence that herbivory-induced responses in plants can be subjected to selection and have an adaptive role by increasing resistance to herbivores.

Natural rubber reduces herbivory and alters the microbiome below ground.

Laticifers are hypothesized to mediate both plant-herbivore and plant-microbe interactions. However, there is little evidence for this dual function. We investigated whether the major constituent of natural rubber, cis-1,4-polyisoprene, a phylogenetically widespread and economically important latex polymer, alters plant resistance and the root microbiome of the Russian dandelion (Taraxacum koksaghyz) under attack of a root herbivore, the larva of the May cockchafer (Melolontha melolontha). Rubber-depleted transgenic plants lost more shoot and root biomass upon herbivory than normal rubber content near-isogenic lines. Melolontha melolontha preferred to feed on artificial diet supplemented with rubber-depleted rather than normal rubber content latex. Likewise, adding purified cis-1,4-polyisoprene in ecologically relevant concentrations to diet deterred larval feeding and reduced larval weight gain. Metagenomics and metabarcoding revealed that abolishing biosynthesis of natural rubber alters the structure but not the diversity of the rhizosphere and root microbiota (ecto- and endophytes) and that these changes depended on M. melolontha damage. However, the assumption that rubber reduces microbial colonization or pathogen load is contradicted by four lines of evidence. Taken together, our data demonstrate that natural rubber biosynthesis reduces herbivory and alters the plant microbiota, which highlights the role of plant-specialized metabolites and secretory structures in shaping multitrophic interactions.

The spread of infectious asexuality through haploid pollen.

The mechanisms of initiation and transmission of apomixis (asexual reproduction through seeds) in natural plant populations are important for understanding the evolution of reproductive variation. Here, we used the phylogenetic diversity of the genus Boechera (Brassicaceae), together with natural diversity in pollen types produced by apomictic lines, to test whether hybridization triggers the transition to asexuality, and whether a 'triploid bridge' is required for the formation of polyploid apomicts. We performed crosses between diploid sexual recipient and diploid apomictic donor lines and tested whether the mating system (interspecific hybridization vs intraspecific outcrossing) or pollen type (haploid vs diploid) influenced the transmission of apomixis from diploid apomictic donors into sexual recipients. We used genetic markers and flow cytometric analyses of embryo and endosperm in seeds to infer the reproductive mode. Within a single generation, initiation of both diploid and polyploid apomixis in sexual Boechera can occur. Diploid apomixis is transmitted through haploid pollen (infectious asexuality) and polyploids can form through multiple pathways. The three functional elements of apomixis occasionally segregate. Variation in pollen ploidy and the segregation of apomixis elements drive reproductive diversity of hybrids and outcrosses and can be utilized for apomixis initiation in crop breeding programs.

Differential localization of flavonoid glucosides in an aquatic plant implicates different functions under abiotic stress.

Flavonoids may mediate UV protection in plants either by screening of harmful radiation or by minimizing the resulting oxidative stress. To help distinguish between these alternatives, more precise knowledge of flavonoid distribution is needed. We used confocal laser scanning microscopy (cLSM) with the "emission fingerprinting" feature to study the cellular and subcellular distribution of flavonoid glucosides in the giant duckweed (Spirodela polyrhiza), and investigated the fitness effects of these compounds under natural UV radiation and copper sulphate addition (oxidative stress) using common garden experiments indoors and outdoors. cLSM "emission fingerprinting" allowed us to individually visualize the major dihydroxylated B-ring-substituted flavonoids, luteolin 7-O-glucoside and luteolin 8-C-glucoside, in cross-sections of the photosynthetic organs. While luteolin 8-C-glucoside accumulated mostly in the vacuoles and chloroplasts of mesophyll cells, luteolin 7-O-glucoside was predominantly found in the vacuoles of epidermal cells. In congruence with its cellular distribution, the mesophyll-associated luteolin 8-C-glucoside increased plant fitness under copper sulphate addition but not under natural UV light treatment, whereas the epidermis-associated luteolin 7-O-glucoside tended to increase fitness under both stresses across chemically diverse genotypes. Taken together, we demonstrate that individual flavonoid glucosides have distinct cellular and subcellular locations and promote duckweed fitness under different abiotic stresses.