Transcriptome analysis and metabolic profiling reveal the key role of α-linolenic acid in dormancy regulation of European pear.

Gilad Gabay,Yardena Dahan,Moshe A Flaishman,Yonatan Elkind,Adi Faigenboim,Maxim Itkin,Yacov Izhaki,Sergey Malitsky

doi:10.1093/jxb/ery405

Abstract

Deciduous trees require sufficient chilling during winter dormancy to grow. To decipher the dormancy-regulating mechanism, we carried out RNA sequencing (RNA-Seq) analysis and metabolic profiling of European pear (Pyrus communis L.) vegetative buds during the dormancy phases. Samples were collected from two cultivars that differed greatly in their chilling requirements: 'Spadona' (SPD), a low chilling requirement cultivar; and Harrow Sweet (HS), a high chilling requirement cultivar. Comparative transcriptome analysis revealed >8500 differentially expressed transcripts; most were related to metabolic pathways. Out of 174 metabolites, 44 displayed differential levels in both cultivars, 38 were significantly changed only in SPD, and 15 only in HS. Phospholipids were mostly accumulated at the beginning of dormancy, sugars between before dormancy and mid-dormancy, and fatty acids, including α-linolenic acid, at dormancy break. Differentially expressed genes underlying previously identified major quantitative trait loci (QTLs) in linkage group 8 included genes related to the α-linolenic acid pathway, 12-oxophytodienoate reductase 2-like, and the DORMANCY-ASSOCIATED MADS-BOX (DAM) genes, PcDAM1 and PcDAM2, putative orthologs of PpDAM1 and PpDAM2, confirming their role for the first time in European pear. Additional new putative dormancy-related uncharacterized genes and genes related to metabolic pathways are suggested. These results suggest the crucial role of α-linolenic acid and DAM genes in pear bud dormancy phase transitions.

Highlights

Pear (Pyrus) belongs to the Rosaceae family and is of major economic importance in temperate climate regions (Chen et al, 2014; Yamamoto and Terakami, 2016)
These results suggest the crucial role of α-linolenic acid and DORMANCY-ASSOCIATED MADS-BOX (DAM) genes in pear bud dormancy phase transitions
Expression of genes underlying QTLs related to timing of vegetative budbreak Candidate genes were sought within the overall mean QTL region in linkage groups (LGs) 5 (Fig. 6A), 8 (Fig. 6B), 9 (Fig. 6C), 13 (Fig. 6D), and 15 (Fig. 6E) which were detected in Gabay et al (2018).Within the major QTL interval in LG8, explaining 28% of the phenotypic variance, we identified a total of 92 transcripts on scaffold

Summary

Introduction

Pear (Pyrus) belongs to the Rosaceae family and is of major economic importance in temperate climate regions (Chen et al, 2014; Yamamoto and Terakami, 2016). Dormancy is an evolutionary mechanism developed in temperate regions to adapt to severe cold climate conditions. Dormancy break occurs when a sufficient number of chilling hours (chilling units=CUs), to which deciduous trees are exposed during endodormancy,have accumulated (Anderson et al.,1986;Heide and Prestrud, 2005). Chilling requirements define the number of CUs needed for the tree to undergo budbreak in the spring, when the climate conditions are suitable for active vegetative growth. Individuals with a high chilling requirement that grow in warm areas where CU accumulation is not sufficient will undergo dormancy break at a later stage; this will affect their vegetative growth, essential for flower and fruit development (Erez and Lavee, 1971; Gabay et al, 2017)

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Discussion

Conclusion