The expression of<i>CBF</i>genes at<i>Fr-2</i>locus is associated with the level of frost tolerance in Bulgarian winter wheat cultivars

Abstract

The regulation of the majority of cold-regulated genes in plants is mediated by <i>CBF</i> (<i>C-repeat binding factors</i>) transcription factor family. Natural differences in frost tolerance (FT) of wheat have been mapped to the <i>Fr-2</i> (<i>Frost Resistance-2</i>) locus on chromosome group 5 and are associated with variation in threshold induction temperatures and/or transcript levels of <i>CBF</i> genes. This study used real-time reverse-transcription polymerase chain reaction (qRT-PCR) to compare the relative expression levels of four <i>T. aestivum CBF</i> genes (<i>TaCBF15.2, TaCBFA19, TaCBFA2</i> and <i>TaCBFD21</i>) in crown tissue of two Bulgarian hexaploid winter wheat cultivars (Milena and Russalka) with distinct levels of low-temperature (LT) tolerance but same vernalization requirement, and the spring cultivar Chinese Spring. The transcription profiles of the selected <i>TaCBF</i> genes showed that they are induced by cold treatment at 2 °C. Analysis of transcript abundance revealed that the four <i>TaCBF</i> genes were expressed at higher levels in the frost tolerant Milena than in the susceptible Russalka. Largest differences (fivefold and fourfold) in expression levels between both winter cultivars were observed in two of the analysed genes, <i>TaCBF15.2</i> and <i>TaCBFA19</i>, respectively. The higher steady-state expression levels of <i>TaCBF</i> genes before the onset of the LT treatment in Milena, combined with stronger induction by cold treatment, suggest that these molecular responses to LT are associated with superior FT development capacity. The results expand our understanding of the molecular mechanisms underlying LT acclimation in Bulgarian wheat and can be used for development of functional markers for improvement of FT wheat-breeding programmes.