How anthocyanin mutants respond to stress: the need to distinguish between stress tolerance and maximal vigour

Background: Anthocyanins are produced by plants in response to diverse stresses. Mutants that block the anthocyanin biosynthetic pathway (ABP) at various steps can easily be compared across numerous abiotic stresses. Hypothesis: Anthocyanins or their precursors are required for stress tolerance. Thus, ABP loss-of-function mutants should have proportionately lower fitness than wildtype plants under stress, compared with benign conditions. In contrast, a decrease in maximal vigour - the general capacity for growth and fecundity - should be most pronounced under benign conditions that allow luxuriant growth by the most vigorous genotypes. Tests: Determine whether, under stressful conditions, ABP loss-of-function mutants have relatively lower fitness than wildtype plants. Also, test for reduced maximal vigour by determining whether ABP mutants have comparatively decreased fitness under optimal (\u27benign\u27) growing conditions. Organism: Arabidopsis thaliana loss-of-function mutants (representing all steps in the ABP), as well as wildtype plants, in two genetic backgrounds. Methods: We grew plants under near-optimal conditions and five stress treatments (UV-B, drought, cold, low Ca:Mg, high Ni). We estimated relative fitness as an individual\u27s lifetime fertility, relative to the mean wildtype fertility in a given treatment. Results: Stress treatments significantly reduced lifetime fertility of wildtype and mutant lines. Wildtypes outperformed anthocyanin-deficient mutants under benign conditions, but as the stress increased, the difference between wildtype and mutant fitness diminished. Fitness did not increase with a mutation\u27s sequential position in the ABP, nor was there an effect of the ability to produce flavonols on fertility. Conclusions: Mutations in the ABP did not reduce stress tolerance. Rather, the loss of ABP function reduced maximal vigour, most evidently in near-optimal growth conditions. © 2010 Eric J. von Wettberg

Early Developmental Responses to Seedling Environment Modulate Later Plasticity to Light Spectral Quality

Correlations between developmentally plastic traits may constrain the joint evolution of traits. In plants, both seedling de-etiolation and shade avoidance elongation responses to crowding and foliage shade are mediated by partially overlapping developmental pathways, suggesting the possibility of pleiotropic constraints. To test for such constraints, we exposed inbred lines of Impatiens capensis to factorial combinations of leaf litter (which affects de-etiolation) and simulated foliage shade (which affects phytochrome-mediated shade avoidance). Increased elongation of hypocotyls caused by leaf litter phenotypically enhanced subsequent elongation of the first internode in response to low red∶far red (R∶FR). Trait expression was correlated across litter and shade conditions, suggesting that phenotypic effects of early plasticity on later plasticity may affect variation in elongation traits available to selection in different light environments

Genetic Patterns of Domestication in Pigeonpea (Cajanus cajan (L.) Millsp.) and Wild Cajanus Relatives

Pigeonpea (Cajanus cajan) is an annual or short-lived perennial food legume of acute regional importance, providing significant protein to the human diet in less developed regions of Asia and Africa. Due to its narrow genetic base, pigeonpea improvement is increasingly reliant on introgression of valuable traits from wild forms, a practice that would benefit from knowledge of its domestication history and relationships to wild species. Here we use 752 single nucleotide polymorphisms (SNPs) derived from 670 low copy orthologous genes to clarify the evolutionary history of pigeonpea (79 accessions) and its wild relatives (31 accessions). We identified three well-supported lineages that are geographically clustered and congruent with previous nuclear and plastid sequence-based phylogenies. Among all species analyzed Cajanus cajanifolius is the most probable progenitor of cultivated pigeonpea. Multiple lines of evidence suggest recent gene flow between cultivated and non-cultivated forms, as well as historical gene flow between diverged but sympatric species. Evidence supports that primary domestication occurred in India, with a second and more recent nested population bottleneck focused in tropical regions that is the likely consequence of pigeonpea breeding. We find abundant allelic variation and genetic diversity among the wild relatives, with the exception of wild species from Australia for which we report a third bottleneck unrelated to domestication within India. Domesticated C. cajan possess 75% less allelic diversity than the progenitor clade of wild Indian species, indicating a severe “domestication bottleneck” during pigeonpea domestication

Alternative ground covers and strip-tilling in CBD hemp production

Abstract Objective Little research has been done on managing soil health for large-scale, outdoor hemp production, contributing to the possible overuse of black plastic for weed suppression. Our experiment aimed to understand the performance of alternative ground covers including forage crops and hay as well as a less disruptive tilling method called strip-tilling compared to black plastic. Results Yield and soil health data were taken from three experimental plantings from two different outdoor CBD hemp farms in Vermont, USA. We find that hay may be a competitive alternative to black plastic in terms of producing heavier plants. Our research also found that clover seed and hay are both more cost-effective options than black plastic which may sway some farmers to adopt these alternative ground cover options

Correlation of genotype mean plasticity to leaf litter and simulated foliage shade for the CT population.

<p>Plasticity to leaf litter was calculated from measurements made before the imposition of the shade treatment. Plasticity to foliage shade was calculated separately for plants in the bare soil and leaf litter treatments. r values are shown, with * for p<0.05, ** for p<0.01.</p

Effect of leaf litter and simulated foliage shade hypocotyl length.

<p>Values before and after the imposition of the shade treatment are shown. We present means across populations and treatments, with standard errors.</p

Effect of leaf litter and simulated foliage shade on first internode length.

<p>Values before and after the imposition of the shade treatment are shown. We present means across populations and treatments, with standard errors.</p

Effect of leaf litter and simulated foliage shade on total plant height.

<p>Values before and after the imposition of the shade treatment are shown. We present means across populations and treatments, with standard errors.</p

Correlation between genotypic mean plasticity to simulated foliage shade in the bare soil and leaf litter treatments.

<p>Calculations were performed separately for two populations, with r-values for the CT and RI shown respectively. No correlation was significant at p<0.05.</p

Traits affected by leaf litter and R∶FR manipulation at the termination of the experiment.

<p>Leaf litter, R∶FR treatment, and population were fixed effects, with genotype nested within population a random effect. Only traits significantly affected by leaf litter or R∶FR manipulation are shown. Interaction terms with p>0.20 were removed from the models.</p