Characterization of MdMYB68, a suberin master regulator in russeted apples.

Apple russeting is mainly due to the accumulation of suberin in the cell wall in response of defects and damages in the cuticle layer. Over the last decades, massive efforts have been done to better understand the complex interplay between pathways involved in the suberization process in model plants. However, the regulation mechanisms which orchestrate this complex process are still under investigation. Our previous studies highlighted number of transcription factor candidates from the Myeloblastosis (MYB) transcription factor family, which might regulate the suberization in the russeted or suberized apple fruit skin. Among these, we identified MdMYB68, which was co-expressed with number of well-known key suberin biosynthesis genes. Using transient expression in Nicotiana benthamiana and whole gene expression profiling analysis, we showed that MdMYB68 was able to trigger the expression of the globality of the already defined suberin biosynthesis pathway. The lipid content analysis further confirmed that MdMYB68 regulates the deposition of suberin in cell. Furthermore, we also investigate the alteration of the cell wall components and showed that MdMYB68 triggered a massive modification of the hemicellulose and pectins as suggested in our previous work. In summary, we here describe MdMYB68 as a new master regulator of the suberin deposition in apple fruit, and also provide, for the first time, new insights related to the fate of the cell wall during the suberization process. Overall design: In order to draw a consistent picture of the MdMYB68 function, we compared 4 biological replicates of Nicotiana benthamiana leaves infiltrated with Pearleygate103 35S::MdMYB68/pBINP19 and 4 biological replicates of control plants infiltrated with P103empty vector /pBINP19.