Abstract:

A MYB transcription factor（TF）（GenBank accession number：MDP0000894463）was
cloned from Malus × domestica‘Royal Gala’. Sequence analysis showed that the length of this gene
was 729 bp，which encoded 243 amino acids. It was predicted that the molecular mass of this protein was
26.34 kD，and pI was 9.29. Phylogenetic tree indicated that our cloned apple MYB TF exhibited the
highest sequence similarity to Arabidopsis AtMYB73，so named MdMYB73. Analysis of functional
domain showed that the MdMYB73 protein included the conserved R2R3-type MYB domain. Quantitative
real-time PCR（qRT-PCR）analysis demonstrated that the MdMYB73 gene was extensively expressed in
different tissues and organs of apple. Specially，the expression level of MdMYB73 was relatively higher in apple leaves and flowers. Meanwhile，the expression of MdMYB73 was obviously induced by salt stress. In
addition，ectopic expression of MdMYB73 decreased salt stress resistance in Arabidopsis，indicating that
MdMYB73 negatively regulated the salt tolerance. qRT-PCR analysis showed that the expression levels of
salt stress-related genes AtSOS1，AtSOS3 and AtNHX1 were significantly decreased in transgenic
Arabidopsis plants，suggesting that MdMYB73 negatively regulated SOS pathway. Finally，salt-tolerance
assay indicated that overexpression of MdMYB73 remarkably decreased the tolerance of transgenic apple
callus to high salinity，further supporting that MdMYB73 negatively control salt tolerance in apple.

Key words: apple, MYB, MdMYB73, SOS, salt stress, gene expression