Gibberellic acid insensitive mRNA transport in both directions between stock and scion in Malus

The sieve tube in higher plants functions as infrastructure for long-distance transport of nutrients, photoassimilates, and growth regulators including hormones. Recently, it was revealed that some protein and RNA molecules also function as movable growth regulators in the sieve tube. In the case of the mRNA of gibberellic acid insensitive (GAI), the transport evidence was obtained through identification of the overproduced transgene transcript. In this work, we investigated the transport of apple (Malus x domestica cv. Fuji and Malus xiaojinensis) endogenous GAI mRNA by grafting experiments. Each GAI mRNA of scion and stock plants was detected in the graft partners as from 5 days after grafting, indicating that the GAI mRNA moves in both upward and downward directions via the graft union.