The chloroplast-nucleus located WHIRLY1 of barley as master regulator of cross-tolerance towards abiotic and biotic stresses

• Applicants: Dr. Götz Hensel; Professorin Dr. Karin Krupinska
• Subject Area: Plant Breeding and Plant Pathology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 458717903

In order to ensure yield stability, crop plants need to react rapidly to changes in the environment and to acclimate efficiently to multiple stress factors which often occur simultaneously. With regard to its dual localization in chloroplasts and nucleus, the RNA/DNA binding protein WHIRLY is an ideal candidate for perception of stress in the chloroplast and for transfer of plastidic stress-signals to the nucleus. Investigations with transgenic barley lines having altered levels of WHIRLY1 revealed that WHIRLY1 is involved in responsiveness of plants towards abiotic stresses and promotes the resistance towards powdery mildew. Analyses of the expression of selected genes revealed that in a hvwhy1 knockout mutant of barley that has been produced by CRISPR RNA/Cas9 endonuclease technology, revealed that WHIRLY1 is a regulator of well-known stress genes in barley. Studies on mutants of maize and barley furthermore showed that WHIRLY1 is necessary for the development of chloroplasts. In the framework of this project specific motifs of the WHIRLY1 protein being important for stress responses are to be identified. Furthermore, it will be investigated whether the functionality of the WHIRLY1 protein in chloroplast development can be separated from the functionality in stress responses of plants. In the nucleus, WHIRLY1, together with NPR1, is involved in the salicylic acid-dependent activation of PR genes. NPR1 which is a central component of salicylic acid signaling, normally is located in the cytoplasm in form of oligomers. As well WHIRLY1 in chloroplasts forms higher order oligomers. During stress dependent production of SA in connection with redox changes, NPR1 is monomerized and then migrates into the cell nucleus. If the stress perception by WHIRLY1 in the chloroplasts is similar to that by NPR1 in the cytoplasm, it can be assumed that a redox-dependent monomerization of the WHIRLY complex is necessary for the stress dependent transfer from the chloroplasts into the cell nucleus. To test whether the conserved cysteine and a lysine in the WHIRLY domain required for oligomerization are important for WHIRLY1 dependent stress responses of barley, the hvwhy1 KO mutant will be complemented with mutated HvWHIRLY1 sequences and the nonmutated sequence of HvWHIRLY1. The transgenic plants will be characterized with regard to their ability to react to various abiotic stress factors as well as powdery mildew in combination with abiotic stress factors. Based on the results, leaf material will be selected for global gene expression analysis using RNAseq. The aim of these investigations is to identify target genes of WHIRLY1 that are either activated or repressed in a cross-tolerance situation (powdery mildew infection in combination with abiotic stress). Prof. Klaus Humbeck's research group at MLU Halle will investigate whether WHIRLY1 influences the transcription of WHIRLY1 target genes via epigenetic mechanisms.

• DFG Programme: Research Grants