Plant development affects the cold-induced expression of plant defence-related transcripts in winter wheat

Abstract

In winter cereals, low temperature hardening, plant age and genotype are known to influence the expression of resistance to snow mould diseases. A study was undertaken to determine the effects of genotype, plant age and duration of cold hardening on the temporal expression of the PR-protein and other defence-related protein transcripts under controlled environment conditions, and in the field during autumn, winter, and early spring. The plant defence-related proteins studied were classified into two groups based on their patterns of expression. The first group consisted of γ-thionin, chitinase, lipid transfer protein (LTP) and phenylalanine ammonia lyase (PAL) whereby transcript levels increased to maximum levels during November–December, but decreased gradually throughout the winter and early spring. Higher transcript levels were observed in late seeded treatments compared with early seeded treatments. Under controlled conditions, transcript levels accumulated rapidly in response to hardening, reaching maximum levels following 1-week and generally maintained levels throughout the hardening treatments. The second group consisted of β-1,3-glucanase, peroxidase and PR-1a whose transcripts increased to maximum levels in the field during November–December, then fluctuated throughout the winter and early spring. Higher transcript levels were observed in early seeded treatments compared to later seeded treatments. Under controlled environment conditions, these transcripts gradually accumulated in response to hardening at 2°C and reached maximum levels after 6 weeks. PR-1a, PAL, and LTP transcript levels were generally higher in the snow mould resistant cultivars PI181268 and D+ throughout the winter and early spring compared to the cold-hardy, snow mould susceptible cultivar, Norstar. Conversely the chitinase and γ-thionin transcripts were expressed at higher levels in the susceptible cultivar Norstar. These results demonstrate that the temporal expression of cold-induced, plant defence-related transcripts in winter wheat is differentially regulated among genotypes and during different plant development stages, and are the first to implicate LTPs in the expression of genotypic-based snow mould resistance in wheat. Potential plant defence signalling pathways involved in snow mould resistance induced at low temperatures during natural acclimation of winter wheat are discussed.