Over-expression of the apple gene MpNPR1 causes increased disease resistance in Malus x domestica

The NPR1 gene is thought to be pivotal in the defense cascade caused by systemic acquired resistance and by R gene resistance in plants. Its over-expression in Arabidopsis and rice has resulted in increased disease resistance and elevated PR-gene expression. An NPR1 homolog, MpNPR1, was cloned from Malus x domestica and over-expressed in two apple cultivars, 'Galaxy' and M26. Leaf pieces were transformed with MpNPR1 cDNA under the control of the Pin2 or CaMV35S promoter using Agrobacterium tumefaciens strain EHA105. PCR analysis confirmed the transgene integration in ca. 20 events for each construct in each cultivar. Over-expression of MpNPR1 mRNA was shown by RT-PCR. Activation of some PR proteins (PR1, PR8, PR10, TPR1) was also demonstrated. Resistance to the serious bacterial disease, fire blight, was evaluated in growth chamber by inoculation of the shoot tips of 30-cm high own-rooted potted plants with the virulent strain Ea273 of Erwinia amylovora. In the initial test, 'Galaxy' clones with an additional copy of MpNPR1 had shoot length infected of 17.5 to 35.5% compared with 80.0% in the control 'Galaxy' plants. MpNPR1-over-expressing 'Galaxy' clones are being propagated for field trials. They are also being evaluated for resistance to other important diseases of apple. Resistance due to over-expression of a native apple gene is likely to be more acceptable to regulators, growers, and consumers than use of heterologous genes. Acceptance will also be facilitated by avoidance or excision of antibiotic-resistance marker genes.

Duke Scholars

Author Sheng-Yang He Biology