Revealing the Genetic Components Responsible for the Unique Photosynthetic Stem Capability of the Wild Almond Prunus arabica (Olivier) Meikle.

Hillel Brukental,Adi Doron-Faigenboim,Doron Holland,Irit Bar-Ya’Akov,Rotem Harel-Beja,Tamar Azoulay-Shemer,Ziv Attia

doi:10.3389/fpls.2021.779970

Hillel Brukental, Adi Doron-Faigenboim + Show 5 more

Open Access

https://doi.org/10.3389/fpls.2021.779970

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Abstract

Almond [Prunus dulcis (Mill.) D. A. Webb] is a major deciduous fruit tree crop worldwide. During dormancy, under warmer temperatures and inadequate chilling hours, the plant metabolic activity increases and may lead to carbohydrate deficiency. Prunus arabica (Olivier) Meikle is a bushy wild almond species known for its green, unbarked stem, which stays green even during the dormancy period. Our study revealed that P. arabica green stems assimilate significantly high rates of CO2 during the winter as compared to P. dulcis cv. Um el Fahem (U.E.F.) and may improve carbohydrate status throughout dormancy. To uncover the genetic inheritance and mechanism behind the P. arabica stem photosynthetic capability (SPC), a segregated F1 population was generated by crossing P. arabica to U.E.F. Both parent’s whole genome was sequenced, and SNP calling identified 4,887 informative SNPs for genotyping. A robust genetic map for U.E.F. and P. arabica was constructed (971 and 571 markers, respectively). QTL mapping and association study for the SPC phenotype revealed major QTL [log of odd (LOD) = 20.8] on chromosome 7 and another minor but significant QTL on chromosome 1 (LOD = 3.9). As expected, the P. arabica allele in the current loci significantly increased the SPC phenotype. Finally, a list of 64 candidate genes was generated. This work sets the stage for future research to investigate the mechanism regulating the SPC trait, how it affects the tree’s physiology, and its importance for breeding new cultivars better adapted to high winter temperatures.

Highlights

The data indicate that P. arabica assimilated CO2 through its green stems during all year, while similar 1-year-old stems of U.E.F. assimilation capacity is almost null
Some fluctuations observed between the different seasons, pronounced high CO2 assimilation rates were found in P. arabica stem during the whole year (Figure 1E)
P. arabica stem transpiration rate is relatively low in the dormancy phase and gradually increases until it peaks in October (1.2 ± 0.18 in January to 5 ± 0.7 mmol H2O m−2 s−1 in October)

Summary

Introduction

As a deciduous fruit tree, it enters dormancy during early winter and renews growth following the fulfillment of a variety-specific period of exposure to low temperatures, known as chilling requirements (CR) and adequate heat requirements. Carbohydrates are consumed, and intense starch synthesis occurs These changes lead to soluble carbohydrate (SC) deficiency in the buds during the period of flowering and fruit set, which results in disruptive flowering that may reduce the yield (Tixier et al, 2017; Fernandez et al, 2018; Guo et al, 2021). Climate-changing trends emphasize the urgent need for deciduous fruit crops to gain more plasticity (Gradziel et al, 2001), for maintaining their non-structural carbohydrate (NSC) reserves in warmer winters (Atkinson et al, 2013; Zwieniecki et al, 2015)

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