Zhang X H, Chiang V L
Plant Biotechnology Research Center, School of Forestry and Wood Products, Michigan Technological University, Houghton 49931, USA.
Plant Physiol. 1997 Jan;113(1):65-74. doi: 10.1104/pp.113.1.65.
Two genomic sequences encoding 4-coumarate:coenzyme A ligase (4CL; EC 6.2.1.12) in loblolly pine (Pinus taeda L.) were cloned. Both sequences contained three introns and four exons with identical coding sequences predicting 537 amino acids. Two of the three introns in these two clones were different both in sequence and in length. Sequences of both 4CL clones were found in all nine megagametophyte DNAs tested, providing genetic evidence that these two 4CL genomic sequences are nonallelic genes. Our analyses suggest that there are at least two distinct, intron-containing 4CL genes, at least one of which is transcribed into 4CL mRNA in developing xylem tissue of loblolly pine. The levels of 4CL gene transcription in xylem were influenced by compressional stress, resulting in an elevated 4CL enzyme activity with 4-coumaric acid. 4CL enzyme activity with ferulic acid remained unchanged, whereas with caffeic acid it was significantly inhibited. Exogenously applied trans-cinnamic acid in the protein extracts from normal wood xylem caused inhibition of 4CL activity toward caffeic acid similar to that under compressional stress. The implications of this cinnamic acid-modulated effect on 4CL enzyme activities toward different substrates in regulating monolignol synthesis in xylem under compressional stress are discussed.
克隆了编码火炬松（Pinus taeda L.）中4-香豆酸：辅酶A连接酶（4CL；EC 6.2.1.12）的两个基因组序列。两个序列均包含三个内含子和四个外显子，其编码序列相同，预测有537个氨基酸。这两个克隆中三个内含子中的两个在序列和长度上均不同。在所有测试的九个大孢子体DNA中均发现了两个4CL克隆的序列，这提供了遗传证据，表明这两个4CL基因组序列是非等位基因。我们的分析表明，至少有两个不同的、含内含子的4CL基因，其中至少一个在火炬松发育中的木质部组织中转录为4CL mRNA。木质部中4CL基因的转录水平受压缩应力影响，导致4CL酶对4-香豆酸的活性升高。4CL酶对阿魏酸的活性保持不变，而对咖啡酸的活性则受到显著抑制。在正常木材木质部的蛋白质提取物中外源施加反式肉桂酸会导致4CL对咖啡酸的活性受到抑制，类似于在压缩应力下的情况。本文讨论了这种肉桂酸调节作用对4CL酶对不同底物的活性在调节压缩应力下木质部中单木质醇合成的影响。
