Microbe-dependent heterosis in maize

Authors: WAGNER, MAGGIE - University Of Kansas; TANG, CLARA - North Carolina State University; SALVATO, FERNANDA - North Carolina State University; CLOUSE, KAYLA - University Of Kansas; BARTLETT, ALEXANDRIA - North Carolina State University; Sermons, Shannon; HOFFMANN, MARK - North Carolina State University; Balint-Kurti, Peter; KLEINER, MANUEL - North Carolina State University

Submitted to: Nature
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: Heterosis , or hybrid vigor, describes the phenomenon of hybrids being much more vigorous than either of their inbred parents. Heterosis is the basis of the maize breeding industry and underlies much of the improved agricultural production experienced in the US over the past century. However, the basis of heterosis remains mysterious. In this study we show that heterosis in a specific maize cross is not expressed in the absence of environmental microbes. This suggests that part of heterosis is due to the interaction of the maize plant with its microbiome.

Technical Abstract: Hybrids account for nearly all commercially planted varieties of maize and many other crop plants, because crosses between inbred lines of these species produce F1 offspring that greatly outperform their parents. The mechanisms underlying this phenomenon, called heterosis or hybrid vigor, are not well understood despite over a century of intensive research (Birchler et al. 2003). The leading hypotheses—which focus on quantitative genetic mechanisms (dominance, overdominance, and epistasis) and molecular mechanisms (gene dosage and transcriptional regulation)—have been able to explain some but not all of the observed patterns of heterosis (Stuber et al. 1992; Birchler 2015). However, possible ecological drivers of heterosis have largely been ignored. Here we show that heterosis of root biomass and germination in maize is strongly dependent on the belowground microbial environment. We found that, in some cases, inbred lines perform as well by these criteria as their F1 offspring under sterile conditions, but that heterosis can be restored by inoculation with a simple community of seven bacterial strains. We observed the same pattern for seedlings inoculated with autoclaved vs. live soil slurries in a growth chamber, and for plants grown in fumigated vs. untreated soil in the field. Together, our results demonstrate a novel, ecological mechanism for heterosis whereby soil microbes generally impair the germination and early growth of inbred but not hybrid maize.