EXPRESSION OF GENES FOR PHENYLALANINE AMMONIA-LYASE AND 8-HYDROXY-3-METHYLGLUTARYL COA REDUCTASE IN AGED POTATO-TUBERS INFECTED WITH PHYTOPHTHORA-INFESTANS
H. Yoshioka et al., EXPRESSION OF GENES FOR PHENYLALANINE AMMONIA-LYASE AND 8-HYDROXY-3-METHYLGLUTARYL COA REDUCTASE IN AGED POTATO-TUBERS INFECTED WITH PHYTOPHTHORA-INFESTANS, Plant and Cell Physiology, 37(1), 1996, pp. 81-90
In comparison with tissues of unaged potato tubers, tissues of aged tu
bers rapidly express features of resistance, such as hypersensitive ce
ll death, browning and the accumulation of phytoalexins in response to
infection by an incompatible race of Phytophthora infestans. Expressi
on of two putative defense genes, namely, genes for 3-hydroxy-3-methyl
glutaryl CoA reductase (HMGR) and phenylalanine ammonia-lyase (PAL), a
nd the activities of the corresponding enzymes were determined in aged
, inoculated potato discs. The level of HMGR activity was higher after
inoculation with an incompatible than with a compatible race of the p
athogen. The levels of the transcripts in the total RNA were, however,
nearly identical in both cases. When we examined polysomal RNA, we fo
und an enhanced level of transcripts for HMGR only in tissues that had
been infected with the incompatible race. Furthermore, comparison of
the patterns of distribution of HMGR mRNA associated with polysomes in
two gradients revealed modulation of HMGR at the level of initiation
of translation. These results suggest that the activity of HMGR in age
d potato tubers that have been attacked by P. infestans might be regul
ated, in part, at the post-transcriptional level in a race-cultivar-sp
ecific manner. By contrast, the levels of PAL mRNA in both the total a
nd the polysomal RNA fractions, as well as the enzymatic activity, wer
e higher in the incompatible than in the compatible interaction. The r
esults suggest that the activity of PAL is regulated differentially at
the transcriptional level during the interactions.