The thesis is organized in six chapters: Chapter I provides an introduction to NAC transcription factors (TFs), including the regulation of NAC TFs and their functions in abiotic and biotic stresses. Recently, several reports have highlighted the NAC TF family for their potential to improve plant stress tolerance. However, despite recent progress in characterisation of the NAC TF family, many questions regarding the function of individual NAC TFs remain open. This study, therefore, arose in a wish to provide an example in barley to understand function of the HvNAC6 TF in response to biotic and abiotic stress. Chapter II is also part of the introduction for the thesis, and represents a review chapter discusses the challenges and the prospects for genetically engineering for disease resistance. My contribution comprised reviewing the progress in understanding the regulatory mechanisms of hormones and transcription factors in plant immunity, which provides an essential foundation before new strategies for developing transgenic resistance can be designed.
The following chapters describe the experimental work and results achieved during the PhD study. Chapters III and IV are two manuscripts presenting the study of barley HvNAC6 TF in the barleyBlumeria graminis f. sp. hordei (Bgh) interaction and in relation to drought response. A reverse genetic approach was used to generate stable knock-down barley plants by RNA-interference (RNAi). Therefore, HvNAC6 RNAi plants generated by Agrobacterium-mediated transformation methods could be used to study stress responses at the whole-plant level. The abscisic acid (ABA) and salicylic acid (SA) levels were measured during Bgh infection to investigate the involvement of these hormones and TF in the basal resistance. HvNAC6 RNAi plants were also subjected to dehydration. Gene expression analysis was used to investigate the interaction of ABA and HvNAC6in response to drought stress. Recognition sequences in the promoter region of HvNAC6 were identified to gain insight into the regulation of HvNAC6. Thus, HvNAC6 promoter fused with GUS reporter transgenic plants were generated to exam the cis-acting regulatory of HvNAC6.
Unpublished results not included in either manuscript are presented in Chapter V, which consists experimental data for further investigate the function of HvNAC6 TF in response to Bgh and ABA treatment. The final Chapter VI provides a summarizing discussion on the findings of the PhD study and suggestions for future research are also presented.