Lashbrook C C, Tieman D M, Klee H J
Department of Horticultural Sciences, University of Florida, Gainesville 32611-0690, USA.
Plant J. 1998 Jul;15(2):243-52. doi: 10.1046/j.1365-313x.1998.00202.x.
Ethylene perception in plants is co-ordinated by multiple hormone receptor candidates sharing sequence commonalties with prokaryotic environmental sensor proteins known as two-component regulators. Two tomato homologs of the Arabidopsis ethylene receptor ETR1 were cloned from a root cDNA library. Both cDNAs, termed LeETR1 and LeETR2, were highly homologous to ETR1, exhibiting approximately 90% deduced amino acid sequence similarity and 80% deduced amino acid sequence identity. LeETR1 and LeETR2 contained all the major structural elements of two-component regulators, including the response regulator motif absent in LeETR3, the gene encoding tomato NEVER RIPE (NR). Using RNase protection analysis, the mRNAs of LeETR1, LeETR2 and NR were quantified in tissues engaged in key processes of the plant life cycle, including seed germination, shoot elongation, leaf and flower senescence, floral abscission, fruit set and fruit ripening. LeETR1 was expressed constitutively in all plant tissues examined. LeETR2 mRNA was expressed at low levels throughout the plant but was induced in imbibing tomato seeds prior to germination and was down-regulated in elongating seedlings and senescing leaf petioles. NR expression was developmentally regulated in floral ovaries and ripening fruit. Notably, hormonal regulation of NR was highly tissue-specific. Ethylene biosynthesis induced NR mRNA accumulation in ripening fruit but not in elongating seedlings or in senescing leaves or flowers. Furthermore, the abundance of mRNAs for all three LeETR genes remained uniform in multiple plant tissues experiencing marked changes in ethylene sensitivity, including the cell separation layer throughout tomato flower abscission.
植物中的乙烯感知由多种激素受体候选物协调，这些候选物与被称为双组分调节因子的原核环境传感器蛋白具有序列共性。从根cDNA文库中克隆了拟南芥乙烯受体ETR1的两个番茄同源物。这两个cDNA，分别称为LeETR1和LeETR2，与ETR1高度同源，推导的氨基酸序列相似性约为90%，推导的氨基酸序列同一性为80%。LeETR1和LeETR2包含双组分调节因子的所有主要结构元件，包括LeETR3中不存在的反应调节基序，LeETR3是编码番茄永不成熟（NR）的基因。使用核糖核酸酶保护分析，对LeETR1、LeETR2和NR的mRNA在参与植物生命周期关键过程的组织中进行了定量，这些过程包括种子萌发、茎伸长、叶片和花朵衰老、花脱落、坐果和果实成熟。LeETR1在所有检测的植物组织中组成性表达。LeETR2 mRNA在整个植物中低水平表达，但在吸水的番茄种子萌发前被诱导，在伸长的幼苗和衰老的叶柄中被下调。NR表达在花子房和成熟果实中受到发育调控。值得注意的是，NR的激素调节具有高度的组织特异性。乙烯生物合成在成熟果实中诱导NR mRNA积累，但在伸长的幼苗、衰老的叶片或花朵中则不然。此外，在乙烯敏感性发生显著变化的多个植物组织中，包括整个番茄花脱落过程中的细胞分离层，所有三个LeETR基因的mRNA丰度保持一致。
