T‐DNA gene 5 of Agrobacterium modulates auxin response by autoregulated synthesis of a growth hormone antagonist in plants.
T‐DNA gene 5 of Agrobacterium modulates auxin response by autoregulated synthesis of a growth hormone antagonist in plants.
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农杆菌的 T-DNA 基因 5 通过植物中生长激素拮抗剂的自动调节合成来调节生长素反应。
作者：
H. Korber;N. Strizhov;Dorothee Staiger;Joachim Feldwisch;O. Olsson;Göran Sandberg;Klaus Palme;Jeff Schell;C. Koncz
农杆菌Ti质粒转移DNA （T‐DNA）携带的癌基因编码植物生长因子、生长素和细胞分裂素的合成，并诱导植物肿瘤的发生。其他T - DNA基因调节肿瘤生长的方式尚不清楚。为了确定T - DNA基因5的功能，我们在大肠杆菌中表达了其编码区。基因5编码蛋白（26 kDa）的合成与色氨酸转化为吲哚- 3 -乳酸（ILA）（一种生长素类似物）增加28倍相关。嵌合基因5构建体在转基因烟草中的表达导致ILA的过量产生，促进了未分化组织的新梢形成，提高了发芽幼苗对外源生长素抑制作用的耐受性。基因5在植物中的启动子分析表明，该基因的表达受植物生长素的诱导，且局限于维管韧皮部细胞。生长素调控所需的顺式调控元件和基因5的韧皮部特异性表达被定位到一个90 bp的启动子区域，该区域携带几种生长素诱导的植物启动子共有的DNA序列基序，以及一个核因子Ax‐1的结合位点。研究发现，ILA抑制了基因5启动子对生长素的诱导，并与吲哚- 3 -乙酸（IAA）在体外结合纯化的细胞生长素结合蛋白上竞争。因此，我们认为ILA可以自动调节其自身的合成，从而调节植物的许多生长素反应。
Oncogenes carried by the transferred DNA (T‐DNA) of Agrobacterium Ti plasmids encode the synthesis of plant growth factors, auxin and cytokinin, and induce tumour development in plants. Other T‐DNA genes regulate the tumorous growth in ways that are not yet understood. To determine the function of T‐DNA gene 5, its coding region was expressed in Escherichia coli. Synthesis of the gene 5 encoded protein (26 kDa) correlated with a 28‐fold increase in conversion of tryptophan to indole‐3‐lactate (ILA), an auxin analogue. Expression of chimeric gene 5 constructs in transgenic tobacco resulted in overproduction of ILA that enhanced shoot formation in undifferentiated tissues and increased the tolerance of germinating seedlings to the inhibitory effect of externally supplied auxin. Promoter analysis of gene 5 in plants revealed that its expression was inducible by auxin and confined to the vascular phloem cells. cis‐regulatory elements required for auxin regulation and phloem specific expression of gene 5 were mapped to a 90 bp promoter region that carried DNA sequence motifs common to several auxin induced plant promoters, as well as a binding site for a nuclear factor, Ax‐1. ILA was found to inhibit the auxin induction of the gene 5 promoter and to compete with indole‐3‐acetic acid (IAA) for in vitro binding to purified cellular auxin binding proteins. It is suggested therefore that ILA autoregulates its own synthesis and thereby modulates a number of auxin responses in plants.