Transcriptome analysis of the vernalization response in barley (Hordeum vulgare) seedlings.

Aaron G Greenup,Sandra N Oliver,Sally A Walford,Ben Trevaskis,Sharyar Sasani,Anthony A Millar,Samuel Hazen

doi:10.1371/journal.pone.0017900

Abstract

Temperate cereals, such as wheat (Triticum spp.) and barley (Hordeum vulgare), respond to prolonged cold by becoming more tolerant of freezing (cold acclimation) and by becoming competent to flower (vernalization). These responses occur concomitantly during winter, but vernalization continues to influence development during spring. Previous studies identified VERNALIZATION1 (VRN1) as a master regulator of the vernalization response in cereals. The extent to which other genes contribute to this process is unclear. In this study the Barley1 Affymetrix chip was used to assay gene expression in barley seedlings during short or prolonged cold treatment. Gene expression was also assayed in the leaves of plants after prolonged cold treatment, in order to identify genes that show lasting responses to prolonged cold, which might contribute to vernalization-induced flowering. Many genes showed altered expression in response to short or prolonged cold treatment, but these responses differed markedly. A limited number of genes showed lasting responses to prolonged cold treatment. These include genes known to be regulated by vernalization, such as VRN1 and ODDSOC2, and also contigs encoding a calcium binding protein, 23-KD jasmonate induced proteins, an RNase S-like protein, a PR17d secretory protein and a serine acetyltransferase. Some contigs that were up-regulated by short term cold also showed lasting changes in expression after prolonged cold treatment. These include COLD REGULATED 14B (COR14B) and the barley homologue of WHEAT COLD SPECIFIC 19 (WSC19), which were expressed at elevated levels after prolonged cold. Conversely, two C-REPEAT BINDING FACTOR (CBF) genes showed reduced expression after prolonged cold. Overall, these data show that a limited number of barley genes exhibit lasting changes in expression after prolonged cold treatment, highlighting the central role of VRN1 in the vernalization response in cereals.

Highlights

In temperate regions, wheat (Triticum spp.) and barley (Hordeum vulgare) can be sown in autumn to grow vegetatively through winter before flowering in spring
C-REPEAT BINDING FACTOR (CBF) genes encode transcription factors that play a critical role in the cold acclimation process [5]
The contigs that showed altered expression after short term cold were predominantly up-regulated, whereas many contigs were down-regulated in the prolonged cold treatment (Figure 2)

Summary

Introduction

Wheat (Triticum spp.) and barley (Hordeum vulgare) can be sown in autumn to grow vegetatively through winter before flowering in spring. The capacity to survive winter frosts is an important trait for autumn-sown wheat and barley varieties grown in regions that experience cold winters [2]–[4]. Tolerance to winter frosts is established through cold acclimation, the process where freezing tolerance increases as temperatures decrease during autumn [5]. Molecular analyses have identified low-temperature responsive genes that are induced during cold acclimation, such as ice crystallisation inhibitors and dehydrins, which protect against freezing damage [5]. CBF genes are rapidly induced by low temperatures to activate genes that contribute to increased freezing tolerance [5]. The FROST RESISTANCE 2 (FR2) locus on chromosome 5A of wheat and barley (5H), which is associated with variation in frost tolerance [6]–

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