Host genotype controls ecological change in the leaf fungal microbiome.

Leaf fungal microbiomes can be fundamental drivers of host plant success, as they contain pathogens that devastate crop plants and taxa that enhance nutrient uptake, discourage herbivory, and antagonize pathogens. We measured leaf fungal diversity with amplicon sequencing across an entire growing season in a diversity panel of switchgrass (Panicum virgatum). We also sampled a replicated subset of genotypes across 3 additional sites to compare the importance of time, space, ecology, and genetics. We found a strong successional pattern in the microbiome shaped both by host genetics and environmental factors. Further, we used genome-wide association (GWA) mapping and RNA sequencing to show that 3 cysteine-rich receptor-like kinases (crRLKs) were linked to a genetic locus associated with microbiome structure. We confirmed GWAS results in an independent set of genotypes for both the internal transcribed spacer (ITS) and large subunit (LSU) ribosomal DNA markers. Fungal pathogens were central to microbial covariance networks, and genotypes susceptible to pathogens differed in their expression of the 3 crRLKs, suggesting that host immune genes are a principal means of controlling the entire leaf microbiome.

A generalist-specialist trade-off between switchgrass cytotypes impacts climate adaptation and geographic range.

Polyploidy results from whole-genome duplication and is a unique form of heritable variation with pronounced evolutionary implications. Different ploidy levels, or cytotypes, can exist within a single species, and such systems provide an opportunity to assess how ploidy variation alters phenotypic novelty, adaptability, and fitness, which can, in turn, drive the development of unique ecological niches that promote the coexistence of multiple cytotypes. Switchgrass, Panicum virgatum, is a widespread, perennial C4 grass in North America with multiple naturally occurring cytotypes, primarily tetraploids (4×) and octoploids (8×). Using a combination of genomic, quantitative genetic, landscape, and niche modeling approaches, we detect divergent levels of genetic admixture, evidence of niche differentiation, and differential environmental sensitivity between switchgrass cytotypes. Taken together, these findings support a generalist (8×)­specialist (4×) trade-off. Our results indicate that the 8× represent a unique combination of genetic variation that has allowed the expansion of switchgrass' ecological niche and thus putatively represents a valuable breeding resource.

Contrasting anther glucose-6-phosphate dehydrogenase activities between two bean varieties suggest an important role in reproductive heat tolerance.

Common beans (Phaseolus vulgaris) are highly sensitive to elevated temperatures, and rising global temperatures threaten bean production. Plants at the reproductive stage are especially susceptible to heat stress due to damage to male (anthers) and female (ovary) reproductive tissues, with anthers being more sensitive to heat. Heat damage promotes early tapetal cell degradation, and in beans this was shown to cause male infertility. In this study, we focus on understanding how changes in leaf carbon export in response to elevated temperature stress contribute to heat-induced infertility. We hypothesize that anther glucose-6-phosphate dehydrogenase (G6PDH) activity plays an important role at elevated temperature and promotes thermotolerance. To test this hypothesis, we compared heat-tolerant and susceptible common bean genotypes using a combination of phenotypic, biochemical, and physiological approaches. Our results identified changes in leaf sucrose export, anther sugar accumulation and G6PDH activity and anther H2 O2 levels and antioxidant-related enzymes between genotypes at elevated temperature. Further, anther respiration rate was found to be lower at high temperature in both bean varieties. Overall, our results support the hypothesis that enhanced male reproductive heat tolerance involves changes in the anther oxidative pentose phosphate pathway, which supplies reductants to critical H2 O2 scavenging enzymes.

Genotypic variation in traits linked to climate and aboveground productivity in a widespread C4 grass: evidence for a functional trait syndrome.

Examining intraspecific variation in growth and function in relation to climate may provide insight into physiological evolution and adaptation, and is important for predicting species responses to climate change. Under common garden conditions, we grew nine genotypes of the C4 species Panicum virgatum originating from different temperature and precipitation environments. We hypothesized that genotype productivity, morphology and physiological traits would be correlated with climate of origin, and a suite of adaptive traits would show high broad-sense heritability (H(2)). Genotype productivity and flowering time increased and decreased, respectively, with home-climate temperature, and home-climate temperature was correlated with genotypic differences in a syndrome of morphological and physiological traits. Genotype leaf and tiller size, leaf lamina thickness, leaf mass per area (LMA) and C : N ratios increased with home-climate temperature, whereas leaf nitrogen per unit mass (Nm ) and chlorophyll (Chl) decreased with home-climate temperature. Trait variation was largely explained by genotypic differences (H(2) = 0.33-0.85). Our results provide new insight into the role of climate in driving functional trait coordination, local adaptation and genetic divergence within species. These results emphasize the importance of considering intraspecific variation in future climate change scenarios.