Phenylpropanoid compounds and disease resistance in transgenic tobacco with altered expression of L-phenylalanine ammonia-lyase.
Tobacco plants over-expressing L-phenylalanine ammonia-lyase (PAL(+)) produce high levels of chlorogenic acid (CGA) and exhibit markedly reduced susceptibility to infection with the fungal pathogen Cercospora nicotianae, although their resistance to tobacco mosaic virus (TMV) is unchanged. Levels of the signal molecule salicylic acid (SA) were similar in uninfected PAL(+) and control plants and also following TMV infection. In crosses of PAL(+) tobacco with tobacco harboring the bacterial NahG salicylate hydroxylase gene, progeny harboring both transgenes lost resistance to TMV, indicating that SA is critical for resistance to TMV and that increased production of phenylpropanoid compounds such as CGA cannot substitute for the reduction in SA levels. In contrast, PAL(+)/NahG plants showed strongly reduced susceptibility to Cercospora nicotianae compared to the NahG parent line. These results are consistent with a recent report questioning the role of PAL in SA biosynthesis in Arabidopsis, and highlight the importance of phenylpropanoid compounds such as CGA in plant disease resistance.
Shadle
Gail L
GL
Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73402, USA.
Wesley
S Varsha
SV
Korth
Kenneth L
KL
Chen
Fang
F
Lamb
Chris
C
Dixon
Richard A
RA
D001203:Ascomycota / Q000472:pathogenicity; D002726:Chlorogenic Acid / Q000378:metabolism; D004198:Disease Susceptibility; D018506:Gene Expression Regulation, Plant; D007113:Immunity, Innate / Q000235:genetics; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D010650:Phenylalanine Ammonia-Lyase / Q000096:biosynthesis* / Q000235:genetics; D010666:Phenylpropionates / Q000378:metabolism*; D010935:Plant Diseases / Q000235:genetics* / Q000382:microbiology / Q000821:virology; D018515:Plant Leaves / Q000378:metabolism / Q000382:microbiology; D030821:Plants, Genetically Modified / Q000201:enzymology* / Q000235:genetics; D020156:Salicylic Acid / Q000378:metabolism; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics* / Q000382:microbiology / Q000821:virology; D014027:Tobacco Mosaic Virus / Q000472:pathogenicity
D010666:Phenylpropionates; D002726:Chlorogenic Acid; D006899:Mixed Function Oxygenases; D010650:Phenylalanine Ammonia-Lyase; D020156:Salicylic Acid