Tamura Ken-ichi, Sanada Yasuharu, Tase Kazuhiro, Yoshida Midori
NARO Hokkaido Agricultural Research Center, 1 Hitsujigaoka, Toyohira, Sapporo 062-8555, Japan.
NARO Hokkaido Agricultural Research Center, 1 Hitsujigaoka, Toyohira, Sapporo 062-8555, Japan.
J Plant Physiol. 2014 Jul 1;171(11):951-8. doi: 10.1016/j.jplph.2014.02.007. Epub 2014 Mar 12.
Metabolism of fructans in temperate grasses dynamically fluctuates before and during winter and is involved in the overwintering activity of plants. We monitored three candidate factors that may be involved in seasonal fructan metabolism in timothy (Phleum pratense): transcription levels of two fructosyltransferase (PpFT1 and PpFT2) genes and one fructan exohydrolase (Pp6-FEH1) gene during fall and winter and under artificially cold conditions. Functional analysis using a recombinant enzyme for PpFT2, a novel fructosyltransferase cDNA, revealed that it encoded sucrose:fructan 6-fructosyltransferase, with enzymatic properties different from previously characterized PpFT1. PpFT1 transcripts decreased from September to December as the amount of fructans increased, whereas PpFT2 transcripts increased in timothy crowns. PpFT2 was transcriptionally more induced than PpFT1 in response to cold and sucrose in timothy seedlings. A rapid increase in Pp6-FEH1 transcripts and increased monosaccharide content were observed in timothy crowns when air temperature was continuously below 0°C and plants were not covered by snow. Transcriptional induction of Pp6-FEH1 by exposure to -3°C was also observed in seedlings. These findings suggest Pp6-FEH1 involvement in the second phase of hardening. PpFT1 and PpFT2 transcription levels decreased under snow cover, whereas Pp6-FEH1 transcription levels were constant, which corresponded with the fluctuation of fructosyltransferase and fructan exohydrolase activities. Inoculation with snow mold fungi (Typhula ishikariensis) increased Pp6-FEH1 transcription levels and accelerated hydrolysis of fructans. These results suggest that transcriptional regulation of genes coding fructan metabolizing enzymes is partially involved in the fluctuation of fructan metabolism during cold acclimation and overwintering.
温带禾本科植物中果聚糖的代谢在冬季之前和冬季期间会动态波动，并参与植物的越冬活动。我们监测了三个可能参与梯牧草（Phleum pratense）季节性果聚糖代谢的候选因素：秋季和冬季以及人工低温条件下两个果糖基转移酶（PpFT1和PpFT2）基因和一个果聚糖外切水解酶（Pp6-FEH1）基因的转录水平。对一种新型果糖基转移酶cDNA PpFT2使用重组酶进行功能分析，结果表明它编码蔗糖：果聚糖6-果糖基转移酶，其酶学特性与先前鉴定的PpFT1不同。随着果聚糖含量的增加，PpFT1转录本从9月到12月减少，而梯牧草冠中的PpFT2转录本增加。在梯牧草幼苗中，PpFT2在转录水平上比PpFT1对低温和蔗糖的诱导反应更强。当气温持续低于0°C且植物未被雪覆盖时，在梯牧草冠中观察到Pp6-FEH1转录本迅速增加且单糖含量增加。在幼苗中也观察到暴露于-3°C会诱导Pp6-FEH1的转录。这些发现表明Pp6-FEH1参与了硬化的第二阶段。在积雪覆盖下，PpFT1和PpFT2的转录水平下降，而Pp6-FEH1的转录水平保持恒定，这与果糖基转移酶和果聚糖外切水解酶活性的波动相对应。接种雪腐真菌（Typhula ishikariensis）会增加Pp6-FEH1的转录水平并加速果聚糖的水解。这些结果表明，编码果聚糖代谢酶的基因的转录调控部分参与了低温驯化和越冬期间果聚糖代谢的波动。
