School of Forest Resources and Environmental Science, Michigan Technological University Houghton, MI 49931-1295 USA.
J Exp Bot. 2012 Sep;63(15):5623-34. doi: 10.1093/jxb/ers217. Epub 2012 Aug 21.
This study describes functional characterization of two putative poplar PHOTOPERIOD RESPONSE 1 (PHOR1) orthologues. The expression and sequence analyses indicate that the two poplar genes diverged, at least partially, in function. PtPHOR1_1 is most highly expressed in roots and induced by short days, while PtPHOR1_2 is more uniformly expressed throughout plant tissues and is not responsive to short days. The two PHOR1 genes also had distinct effects on shoot and root growth when their expression was up- and downregulated transgenically. PtPHOR1_1 effects were restricted to roots while PtPHOR1_2 had similar effects on aerial and below-ground development. Nevertheless, both genes seemed to be upregulated in transgenic poplars that are gibberellin-deficient and gibberellin-insensitive, suggesting interplay with gibberellin signalling. PHOR1 suppression led to increased starch accumulation in both roots and stems. The effect of PHOR1 suppression on starch accumulation was coupled with growth-inhibiting effects in both roots and shoots, suggesting that PHOR1 is part of a mechanism that regulates the allocation of carbohydrate to growth or storage in poplar. PHOR1 downregulation led to significant reduction of xylem formation caused by smaller fibres and vessels suggesting that PHOR1 likely plays a role in the growth of xylem cells.
本研究描述了两个拟南芥 PHOTOPERIOD RESPONSE 1（PHOR1）同源物的功能特征。表达和序列分析表明，这两个杨树基因在功能上至少部分分化。PtPHOR1_1 在根中表达最高，受短日照诱导，而 PtPHOR1_2 在植物组织中均匀表达，不受短日照影响。当它们的表达被转基因上调和下调时，这两个 PHOR1 基因也对地上和地下生长有不同的影响。PtPHOR1_1 的作用仅限于根，而 PtPHOR1_2 对地上和地下发育有类似的影响。然而，这两个基因似乎在赤霉素缺乏和赤霉素不敏感的转基因杨树中上调，表明与赤霉素信号转导相互作用。PHOR1 的抑制导致根和茎中淀粉积累增加。PHOR1 抑制对淀粉积累的影响与根和地上部生长抑制的影响相关，表明 PHOR1 是调节杨树碳水化合物向生长或储存分配的机制的一部分。PHOR1 的下调导致木质部形成显著减少，原因是纤维和导管较小，表明 PHOR1 可能在木质部细胞生长中发挥作用。
