Choi D, Ward B L, Bostock R M
Department of Plant Pathology, University of California, Davis.
Plant Cell. 1992 Oct;4(10):1333-44. doi: 10.1105/tpc.4.10.1333.
Induction of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is essential for the biosynthesis of sesquiterpenoid phytoalexins and steroid derivatives in Solanaceous plants following stresses imposed by wounding and pathogen infection. To better understand this complex step in stress-responsive isoprenoid synthesis, we isolated three classes of cDNAS encoding HMGR (hmg1, hmg2, and hmg3) from a potato tuber library using a probe derived from an Arabidopsis HMGR cDNA. The potato cDNAs had extensive homology in portions of the protein coding regions but had low homology in the 3' untranslated regions. RNA gel blot analyses using gene-specific probes showed that hmg1 was strongly induced in tuber tissue by wounding, but the wound induction was strongly suppressed by treatment of the tissue with the fungal elicitor arachidonic acid or by inoculation with an incompatible or compatible race of the fungal pathogen Phytophtora infestans. The hmg2 and hmg3 mRNAs also accumulated in response to wounding, but in contrast to hmg1, these mRNAs were strongly enhanced by arachidonic acid or inoculation. Inoculation with a compatible race of P. infestans resulted in similar patterns in HMGR gene expression of hmg2 and hmg3 except that the magnitude and rate of the changes in mRNA levels were reduced relative to the incompatible interaction. The differential regulation of members of the HMGR gene family may explain in part the previously reported changes in HMGR enzyme activities following wounding and elicitor treatment. The suppression of hmg1 and the enhancement of hmg2 and hmg3 transcript levels following elicitor treatment or inoculation with the incompatible race parallel the suppression in steroid and stimulation of sesquiterpenoid accumulations observed in earlier investigations. The results are discussed in relation to the hypothesis that there are discrete organizational channels for sterol and sesquiterpene biosynthesis in potato and other Solanaceous species.
在茄科植物受到创伤和病原体感染的胁迫后，诱导3-羟基-3-甲基戊二酰辅酶A还原酶（HMGR）对于倍半萜类植保素和类固醇衍生物的生物合成至关重要。为了更好地理解应激反应类异戊二烯合成中的这一复杂步骤，我们使用源自拟南芥HMGR cDNA的探针，从马铃薯块茎文库中分离出三类编码HMGR的cDNA（hmg1、hmg2和hmg3）。马铃薯cDNA在蛋白质编码区的部分具有广泛的同源性，但在3'非翻译区具有低同源性。使用基因特异性探针进行的RNA凝胶印迹分析表明，hmg1在块茎组织中受到创伤强烈诱导，但用真菌激发子花生四烯酸处理组织或接种真菌病原体致病疫霉的不亲和或亲和小种后，创伤诱导被强烈抑制。hmg2和hmg3 mRNA也响应创伤而积累，但与hmg1相反，这些mRNA被花生四烯酸或接种强烈增强。接种致病疫霉的亲和小种导致hmg2和hmg3的HMGR基因表达出现类似模式，只是相对于不亲和相互作用，mRNA水平变化的幅度和速率降低。HMGR基因家族成员的差异调节可能部分解释了先前报道的创伤和激发子处理后HMGR酶活性的变化。激发子处理或接种不亲和小种后hmg1的抑制以及hmg2和hmg3转录水平的增强与早期研究中观察到的类固醇积累抑制和倍半萜积累刺激平行。结合马铃薯和其他茄科物种中甾醇和倍半萜生物合成存在离散组织通道的假说对结果进行了讨论。
