Engelgau, P. | bioRxiv Science

bioRxiv2023

Apple and banana fruits produce anteiso- and iso-branched-chain esters from newly synthesized precursors

Inhibitors of acetohydroxyacid synthase, the common enzyme of branched-chain amino acid biosynthesis, were applied to ripening apple (Malus xdomestica Borkh.), banana (Musa spp.), and flowering quince (Chaenomeles xsuperba) fruits to discern the contribution of newly synthesized precursors to branched-chain ester formation. After treatment, anteiso- and iso-branched-chain volatiles (i.e., those related to isoleucine, and valine and leucine, respectively) were observed to universally decrease in content. Fruits recovered production following exogenous feeding of branched-chain -ketoacids. Furthermore, apple and banana fruits were capable of metabolizing all three branched-chain -ketoacids to esters. Among free amino acids, only the branched-chain amino acids with correspondingly reduced branched-chain esters had a lesser concentration following treatment with inhibitor. Our results ultimately reject the hypothesis that anteiso- and iso-branched-chain esters are derived from preexisting amino acids and instead support the hypothesis that these esters are the product of de novo precursor biosynthesis. The novel use of these inhibitors also allowed for further investigation of branched-chain volatile biosynthesis, the citramalate synthase pathway, and the importance of precursor availability in fruits. Notably, in Valery banana fruit, ethyl acetate and butyl acetate were found to be dependent on acetohydroxyacid synthase activity for production whereas 1-methylbutyl acetate and 1-methylbutyl butanoate (sec-branched-chain esters) were not. Inhibitor usage on apples also allowed for a sensory study that found that humans can discern the absence of 2-methylbutyl and 2-methylbutanoate esters in apple fruit. Additionally, a population genetics analysis found that there is selection pressure against apples that lack these esters.

biochemistry↗

bioRxiv2020

Composite modeling of leaf shape across shoots discriminates Vitis species better than individual leaves

Premise of studyLeaf morphology is dynamic, continuously deforming during leaf expansion and among leaves within a shoot. We measured leaf morphology from over 200 vines over four years, and modeled changes in leaf shape along the shoot to determine if a composite "shape of shapes" can better capture variation and predict species identity compared to individual leaves. MethodsUsing homologous universal landmarks found in grapevine leaves, we modeled various morphological features as a polynomial function of leaf node. The resulting functions are used to reconstruct modeled leaf shapes across shoots, generating composite leaves that comprehensively capture the spectrum of possible leaf morphologies. ResultsWe found that composite leaves are better predictors of species identity than individual leaves from the same plant. We were able to use composite leaves to predict species identity of previously unassigned vines, which were verified with genotyping. DiscussionObservations of individual leaf shape fail to capture the true diversity between species. Composite leaf shape--an assemblage of modeled leaf snapshots across the shoot--is a better representation of the dynamic and essential shapes of leaves, as well as serving as a better predictor of species identity than individual leaves.

plant biology↗