Induction of phenylpropanoid gene transcripts in oat attacked byErysiphe graminisat 20 °C and 10 °C

• Published in: Physiological and molecular plant pathology 1997-07, Vol.51 (1), p.15-33
• Main Authors: Zhang, L, Robbins, M.P, Carver, T.L.W, Zeyen, R.J
• Format: Article
• Language: English
• ISSN: 0885-5765; 1096-1178
• DOI: 10.1006/pmpp.1997.0092

The time-course of germling development and attempted infection byErysiphe graminis,and of autofluorescent epidermal cell responses to attack by the fungus, was compared in seedling leaves of oat cv. Maldwyn grown and incubated at 10 °C and 20 °C. Incubation at 10 °C approximately doubled the time taken for germling populations to reach a particular developmental stage and increased somewhat the asynchrony of their development. Nevertheless, temperature ultimately had little effect on spore germination, the development of germlings, or on infection success. Northern blot analyses compared transcript accumulation of genes concerned with phenylpropanoid biosynthesis in inoculated and uninoculated leaves incubated at the two temperatures. At both temperatures, transcripts corresponding to phenylalanine ammonia lyase (PAL), S-adenosyl-l-methionine synthetase (SAMS) and an extracellular peroxidase (POX), showed marked but transient accumulations in inoculated leaves. The major accumulations of PAL and SAMS coincided exactly with the maturation of appressoria and the onset of autofluorescent host cell responses, declining as attempted penetration occurred (determined by haustorium formation). At both temperatures POX accumulated slightly later than PAL and SAMS, showing maximal accumulation when the majority of appressoria had stimulated autofluorescence. This is consistent with POX acting on substrata produced by the earlier action of PAL and SAMS. Further transcript analyses of material from 20 °C incubation showed accumulation of a transcript for 4-coumarate CoA ligase coinciding with early appressorial attack. However,E. graminisattack did not induceO-methyltransferase,p-coumaroyl CoA 3-O-methyltransferase or cinnamyl alcohol dehydrogenase, suggesting that transcriptional regulation of these genes may not be involved in the response. Similarly, although a gene for chalcone synthase hybridized to at least two corresponding transcripts in Maldwyn RNA, there was no evidence of their induction byE. graminisattack, and therefore no evidence that products of the flavonoid biosynthetic pathway are involved in the response. The data are compatible with the hypotheses that phenylpropanoid compounds, possibly lignin or lignin-like materials and/or phenylpropanoids esterified to cell wall materials, are producedde novoin response toE. graminisand that they are involved in resistance to attack.