Abstract
During plant domestication and improvement, farmers select for alleles present in wild species that improve performance in new selective environments associated with cultivation and use. The selected alleles become enriched and other alleles depleted in elite cultivars. One important aspect of crop improvement is expansion of the geographic area suitable for cultivation; this frequently includes growth at higher or lower latitudes, requiring the plant to adapt to novel photoperiodic environments. Many crops exhibit photoperiodic control of flowering and altered photoperiodic sensitivity is commonly required for optimal performance at novel latitudes. Alleles of a number of circadian clock genes have been selected for their effects on photoperiodic flowering in multiple crops. The circadian clock coordinates many additional aspects of plant growth, metabolism and physiology, including responses to abiotic and biotic stresses. Many of these clock-regulated processes contribute to plant performance. Examples of selection for altered clock function in tomato demonstrate that with domestication, the phasing of the clock is delayed with respect to the light–dark cycle and the period is lengthened; this modified clock is associated with increased chlorophyll content in long days. These and other data suggest the circadian clock is an attractive target during breeding for crop improvement.
Highlights
The centrality of the circadian clock to photoperiodic flowering has meant that allelic variation of circadian clock genes has contributed to range expansion in many crop species
The circadian clock contributes to the regulation of circadian of growth and metabolism, as well as to abiotic and biotic stress responses [12,13,209]
In Arabidopsis, a clock that resonates with the environmental daylength enhances photosynthesis and biomass accumulation [212]
Summary
About 10,000 years ago, shortly after the end of the most recent ice age, humans began the transition from foraging to farming with extraordinary consequences for both the human domesticators and their domesticated plants and animals, as well as for their non-domesticated counterparts [1]. Only seeds from the best plants are retained for the generation so this loss of diversity increases with each successive generation during the domestication process resulting in a genetic bottleneck The extent of this loss of diversity depends on the population size during the domestication period and the duration of that period [7]. Initial domestication occurs in the environment of the wild progenitor Following this initial domestication, there is frequently a period of range expansion in which successfully domesticated crops are moved through trade into new geographic regions where they encounter novel environmental features, both abiotic and biotic. This range expansion, can be expected to be accompanied by selection for improved performance in these novel environments. The purpose of this review is to consider the evidence that such selection for altered clock function has occurred
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