Molecular mechanism of symbiotic specific gene expression

研究了不同氮素营养条件下紫花苜蓿不同组织中酰脲（尿囊素和尿囊酸）的积累规律。酰胺型豆科植物紫花苜蓿和百脉根木质部汁液中酰脲与天冬酰胺的比值比典型酰脲型豆科植物大豆低14倍。两个编码尿酸酶（EC 1.7.3.3.，结瘤素-35）分离自苜蓿（Medicago sativa）植物的根瘤组织制备的cDNA文库。MsU 2和MsU 9均编码3 0 8个氨基酸的多肽，差异5个氨基酸，推导的氨基酸序列同源性为980/0。这两个cDNA克隆与命名为Nod-35 s的大豆尿酸酶基因在核苷酸和推导的氨基酸序列上的同源性均在800/0以上，表明它们是Nod-35的同源基因。木质部汁液中酰脲的存在和根瘤中尿酸酶的活性证实了尿酸酶基因的作用。原位杂交分析显示，MsU 2和MsU 9只在结节组织感染区的未感染细胞中表达。这两个尿酸酶基因在大豆根瘤中的细胞特异性表达与Nod-35相同。

The profiles of ureide (allantoin and allantoic acid) accumulation under different nitrogen nutrient conditions were surveyed in various tissues of alfalfa, Medicago sativa. The ratios of ureide to asparagine in xylem saps of two amide type legumes, Medicago sativa and Lotus corniculatus were 14 times less than that of a typical ureide type legume, Glycine max. when they are growing with nitrogen-free nutrient solution.Two cDNA clones, MsU2 and MsU9 encoding uricase (EC 1.7.3.3., Nodulin-35) were isolated from a cDNA library prepared from nodule tissues of alfalfa, Medicago sativa, plants. Both MsU2 and MsU9 encoded 3 08 amino acid polypeptides with a difference of 5 amino acids, and the deduced amino acid sequences shared 980/0 homology. Between these two cDNA clones and uricase genes of soybean which were designated as Nod-35s, more than 800/0 identity was observed in nucleotides and deduced amino acid sequences, suggesting that these MsU2 and MsU9 are homologs of Nod-35.Using the reverse transcription-PCR technique, we detected the transcripts of these two genes in almost all tissues of alfalfa. The operation of uricase genes was confirmed by the presence of ureide in the xylem sap and uricase activity in the nodules. In situ hybridization analysis revealed that MsU2 and MsU9 were expressed only in uninfected cells of the infected zone of the nodule tissue. The cell specific-expression of the two uricase genes was observed in an identical manner to that of Nod-35 in soybean nodules.