S01 - Session O9 - II - Identification of transmissible mRNA provides insights into rootstock-induced dwarfing in apple

Authors: Zhen-Hai Han *, Wei Li, Hui Li, Hao-Chen Sun, Yu-Qi Li, Shi-Yao Wang, Yi Wang, Xue-Feng Xu

The wide use of dwarfing rootstocks has led to a steady increase in the efficiency of apple production over the past century. However, the underlying mechanism of rootstock-induced dwarfing is still largely unknown. Here, we assembled genomes for the cultivated apple 'Fuji' and two apple rootstocks, 'M9' (dwarf) and 'MM106' (semi-dwarf). Furthermore, we employed 4-year-old grafted trees as experimental materials and collected shoot samples in two stages for transcriptome analysis: Stage I (early August) and Stage II (mid-May). Based on the genome and transcriptome data, w e have developed a de novo bioinformatical pipeline for detecting mobile mRNAs between rootstocks and scions . For Stage I, we were able to identify 779 and 1069 SNPs in Fuji scions grafted on 'M9' and 'MM106', corresponding to 548 and 631 genes, respectively. For Stage II, we were able to identify 916 and 824 SNPs in Fuji scions grafted on 'M9' and 'MM106', corresponding to 648 and 518 genes, respectively. Among these identified genes, about 30% have more than two supported SNPs. A n auxin inducible gene, MdSAUR76 , was identified as transmissible from rootstocks to scion in Stage I. Lower accumulation of MdSAUR76 mRNA was observed in the scions grafted onto 'M9' than those grafted on 'MM106', which may explain the shorter autumn shoots for scions on 'M9'. In Stage II, we also identified the graft-transmissible gene MdFeronia , which has been reported with a function of promoting flowering. We were able to detect more MdFeronia transcripts in the scions of 'M9' rootstock than those in the scions on 'MM106' rootstock, which may explain scions on 'M9' rootstock always forming more floral buds. These identified transmissible mRNA will provide important guidance for revealing the mechanism of the rootstock-induced dwarfing phenotype.