Change of function of the wheat stress‐responsive transcriptional repressor Ta RAP 2.1L by repressor motif modification

Summary Plants respond to abiotic stresses by changes in gene regulation, including stress‐inducible expression of transcriptional activators and repressors. One of the best characterized families of drought‐related transcription factors are dehydration‐responsive element binding ( DREB ) proteins, known as C‐repeat binding factors ( CBF ). The wheat DREB / CBF gene Ta RAP 2.1L was isolated from drought‐affected tissues using a dehydration‐responsive element ( DRE ) as bait in a yeast one‐hybrid screen. Ta RAP 2.1L is induced by elevated abscisic acid, drought and cold. A C‐terminal ethylene responsive factor‐associated amphiphilic repression ( EAR ) motif, known to be responsible for active repression of target genes, was identified in the Ta RAP 2.1L protein. It was found that Ta RAP 2.1L has a unique selectivity of DNA‐binding, which differs from that of DREB activators. This binding selectivity remains unchanged in a Ta RAP 2.1L variant with an inactivated EAR motif ( Ta RAP 2.1Lmut ). To study the role of the Ta RAP 2.1L repressor activity associated with the EAR motif in planta , transgenic wheat overexpressing native or mutated Ta RAP 2.1L was generated. Overexpression of Ta RAP 2.1L under constitutive and stress‐inducible promoters in transgenic wheat and barley led to dwarfism and decreased frost tolerance. By contrast, constitutive overexpression of the Ta RAP 2.1Lmut gene had little or no negative influence on wheat development or grain yield. Transgenic lines with the Ta RAP 2.1Lmut transgene had an enhanced ability to survive frost and drought. The improved stress tolerance is attributed to up‐regulation of several stress‐related genes known to be downstream genes of DREB / CBF activators.