Identification and Molecular Characterization of a Class I Chitinase Gene (Mhchit1) from Malus hupehensis

Mhchit1, a class I chitinase gene from Malus hupehensis, was cloned, and its expression and functionality in young seedlings were studied. Treatment with salicylic acid, methyl jasmonate, and 1-aminocyclopropane-1-carboxylic acid resulted in the elevation of Mhchit1 transcript levels in leaves, stems, and roots. Infection with Botryosphaeria berengeriana caused an accumulation of Mhchit1 transcripts, with maximum levels at 6 h post-inoculation. Mhchit1 expression was also induced by the apple aphid Aphis citricota. Transgenic tobacco plants that over-expressed Mhchit1 showed enhanced resistance to Botrytis cinerea, relative to wild-type control plants, and were not susceptible to polyethylene glycol. In addition, transcript levels for superoxide dismutase, ascorbate peroxidase, polyphenoloxidase, and phenylalanine ammonia lyase were up-regulated in the transgenic plants. These results suggest that Mhchit1 is not only involved in the SA-signal pathway but also with the jasmonate/ethylene-signal pathway. Our data support the role of Mhchit1 in M. hupehensis as an important part of the plant's defense strategy through promotion of resistance to a number of stress abiotic and biotic factors.