Adaptive evolution of benzoxazinoids in wild emmer wheat, Triticum dicoccoides, at "Evolution Canyon", Mount Carmel, Israel.

Yuval Ben-Abu,Eviatar Nevo,Avigdor Beiles,Dvir Flom,Ruslan Kalendar

doi:10.1371/journal.pone.0190424

Yuval Ben-Abu, Eviatar Nevo + Show 3 more

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https://doi.org/10.1371/journal.pone.0190424

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Abstract

Background"Evolution Canyon" (ECI) at Lower Nahal Oren, Mount Carmel, Israel, is an optimal natural microscale model for unraveling evolution-in-action, highlighting the evolutionary processes of biodiversity evolution, adaptation, and incipient sympatric speciation. A major model organism in ECI is the tetraploid wild emmer wheat, Triticum dicoccoides (TD), the progenitor of cultivated emmer and durum wheat. TD displays dramatic interslope adaptive evolutionary divergence on the tropical, savannoid-hot and dry south-facing, "African" slope (AS), and on the temperate, forested, cool and humid, north-facing, "European" slope (ES), separated on average by 250 m. From the perspective of chemical evolution and metabolomics, it is important to unravel interslope divergence in biologically relevant secondary metabolites between the abutting slope populations. Here, in TD we examined hydroxamic acid (Hx), which is a family of secondary cereal metabolites, and plays a major role in defending the plant against fungi, insects and weeds.ResultsOur examination revealed that higher concentrations of DIBOA and DIMBOA were found in seedlings growing in the same greenhouse from seeds collected from the cool and humid forested ES, whereas the seedlings of seeds collected from the savannoid AS (both in root and shoot tissues), showed no DIMBOA. Remarkably, only DIBOA appears in both shoots and roots of the AS seedlings. It rises to a peak and then decreases in both organs and in seedlings from both slopes. The DIMBOA, which appears only in the ES seedlings, rises to a peak and decreases in the shoot, but increased and remained in a plateau in the root, till the end of the experiment.Conculsions/SignificanceThe results suggest stronger genetic resistance of defense compounds DIBOA and DIMBOA against biotic stresses (fungi and other pathogens) by ES seedlings. However, AS seedlings responded earlier but were to the same biotic stresses. The genetic difference found in AS seedlings was caused by the main adaptive selection in AS, which was against climatic, abiotic stresses, and was weaker, or not at all, against biotic stresses. The distinct genetic interslope differences appear important and is very significant and are elaborated in the discussion.

Highlights

Our examination revealed that higher concentrations of DIBOA and DIMBOA were found in seedlings growing in the same greenhouse from seeds collected from the cool and humid forested European" slope (ES), whereas the seedlings of seeds collected from the savannoid African" slope (AS), showed no DIMBOA
The "Evolution Canyon" (ECI) microsite model is the focus of a long-term research program that began in the Lower Nahal Oren, Mount Carmel, Israel in 1990 and was extended to three additional ECs: Upper Galilee (ECII) [1,2,3], southern Negev desert [2, 4,5] (EC III), and the Golan (ECIV) [4,5,6]
This study showed that the genetics of benzoxazinoid production in two contrasting populations at the AS and ES of wild emmer wheat T. dicoccoide, differ largely and significantly when tested in the same greenhouse, i.e., the same environment

Summary

Introduction

The "Evolution Canyon" (ECI) microsite model is the focus of a long-term research program that began in the Lower Nahal Oren, Mount Carmel, Israel in 1990 and was extended to three additional ECs: Upper Galilee (ECII) [1,2,3], southern Negev desert [2, 4,5] (EC III), and the Golan (ECIV) [4,5,6]. The major environmental stresses on the AS are solar radiation, temperature and drought, all of which are higher on the AS than on the ES, and associated with higher genetic variation, on average, on the AS than on the ES [3, 7, 15, 16]. This microscale pattern of genetic variation positively associating with environmental stress is true locally, such as in ECI, regionally, across Israel, and globally [16]. Ecological stress at a microscale can generally generate regional or global-scale effects of phonemics, genomics and proteomics, reinforcing homeostasis and fitness, thereby suggesting continuity between micro- and macroevolution [1, 7, 16]

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