PHOTOPERIOD RESPONSE 1 (PHOR1)-like Genes Regulate Shoot/root Growth, Starch Accumulation, and Wood Formation in Populus

Document Type


Publication Date



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. © 2012 The Author.

Publication Title

Journal of Experimental Botany