Abstract

The RESPONSIVE TO DEHYDRATION 22 (RD22) gene is a molecular link between abscisic acid (ABA) signalling and abiotic stress responses. Its expression has been used as a reliable ABA early response marker. In Arabidopsis, the single copy RD22 gene possesses a BURP domain also located at the C-terminus of USP embryonic proteins and the beta subunit of polygalacturonases. In grapevine, a RD22 gene has been identified but putative paralogs are also found in the grape genome, possibly forming a large RD22 family in this species. In this work, we searched for annotations containing BURP domains in the Vitis vinifera genome. Nineteen proteins were defined by a comparative analysis between the two genome predictions and RNA-Seq data. These sequences were compared to other plant BURPs identified in previous genome surveys allowing us to reconceive group classifications based on phylogenetic relationships and protein motif occurrence. We observed a lineage-specific evolution of the RD22 family, with the biggest expansion in grapevine and poplar. In contrast, rice, sorghum and maize presented highly expanded monocot-specific groups. The Vitis RD22 group may have expanded from segmental duplications as most of its members are confined to a region in chromosome 4. The inspection of transcriptomic data revealed variable expression of BURP genes in vegetative and reproductive organs. Many genes were induced in specific tissues or by abiotic and biotic stresses. Three RD22 genes were further studied showing that they responded oppositely to ABA and to stress conditions. Our results show that the inclusion of RNA-Seq data is essential while describing gene families and improving gene annotations. Robust phylogenetic analyses including all BURP members from other sequenced species helped us redefine previous relationships that were erroneously established. This work provides additional evidence for RD22 genes serving as marker genes for different organs or stresses in grapevine.

Highlights

  • A plant’s adaptive response to overcome any abiotic or biotic stress requires the initiation of various biochemical and physiological measures, which will allow the organism to survive

  • Since we show that VvRD22c suffers more dramatic differences compared to VvRD22a and VvRD22b in terms of expression and stress responsiveness, this possible small interfering RNAs (siRNA)-induced control may be crucial for VvRD22c expression

  • Our findings suggest that the expansion of RESPONSIVE TO DEHYDRATION 22 (RD22) genes occurred with an increased rate within woody plant lineages

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Summary

Introduction

A plant’s adaptive response to overcome any abiotic or biotic stress requires the initiation of various biochemical and physiological measures, which will allow the organism to survive. Changes in its concentration can lead to a number of adaptations including stomatal closure [2], growth inhibition and senescence or flowering induction, all of which can be regulated at a transcriptional level [3]. These events comprise changes in the expression of hundreds of genes that are influenced by the degree, extent and rate of each stress [4]. The RESPONSIVE TO DEHYDRATION 22 (RD22) protein is induced by an ABA-dependent signalling mechanism, requiring de novo protein synthesis [7]. The Arabidopsis MYC2 ( known as RD22-BP1) and MYB2 transcription factors bind cis-elements in the RD22 promoter and cooperatively activate its transcription in response to drought, salinity and exposure to exogenous ABA [8]

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