Abstract
Expansion of the maize growing area was central for food security in temperate regions. In addition to the suppression of the short-day requirement for floral induction, it required breeding for a large range of flowering time that compensates the effect of South-North gradients of temperatures. Here we show the role of a novel florigen gene, ZCN12, in the latter adaptation in cooperation with ZCN8. Strong eQTLs of ZCN8 and ZCN12, measured in 327 maize lines, accounted for most of the genetic variance of flowering time in platform and field experiments. ZCN12 had a strong effect on flowering time of transgenic Arabidopsis thaliana plants; a path analysis showed that it directly affected maize flowering time together with ZCN8. The allelic composition at ZCN QTLs showed clear signs of selection by breeders. This suggests that florigens played a central role in ensuring a large range of flowering time, necessary for adaptation to temperate areas.
Highlights
Maize was domesticated 9000 years ago in central Mexico from teosinte (Zea mays subsp. parviglumis), a tropical plant that only flowers under short days [1]
We first measured the time from germination to pollen shedding on florets, to the emergence of silks from the ear and the final leaf number which reflects the duration from germination to floral transition, in four experiments in a phenotyping platform and in the field
It is unlikely that the absence of cis-type eQTLs for ZEA CENTRORADIALIS 8 (ZCN8) could depend on insufficient coverage of the genetic diversity, since they were discovered on a large set of diverse inbred lines: 32,758 accessions for 6 Genotyping by Sequencing (GBS) markers, [36] and 30 accessions for 3 Affymetrix Axiom markers [34]
Summary
Maize was domesticated 9000 years ago in central Mexico from teosinte (Zea mays subsp. parviglumis), a tropical plant that only flowers under short days [1]. Maize was domesticated 9000 years ago in central Mexico from teosinte In contrast to its wild ancestor, modern maize shows a large geographic distribution from 0 to 50 ̊ N. Because the time to flowering strongly depends on temperature, it is shorter for a given non-photoperiodic genotype at lower than at higher latitudes of the temperate area. A long intrinsic cycle duration is necessary to counteract this effect in warmest areas, thereby avoiding decreases in cumulated photosynthesis and biomass. A short intrinsic duration is needed in the coolest areas to avoid grain filling to occur in Autumn with low light and temperature [2]. The range of time to flowering in current germplasm typically ranges from 35 to 90 days after sowing in a given site [3]
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