Overexpression of SHORT-ROOT2 transcription factor enhances the outgrowth of mature axillary buds in poplar trees. (2nd February 2022) - Yi, Minglei
Abstract : PtSHR2 overexpression in poplar promotes axillary bud outgrowth below the bud maturation point by disturbing basipetal auxin transport and increasing the ratio of cytokinin to auxin in buds. Abstract: SHORT-ROOT (SHR) transcription factors play important roles in asymmetric cell division and radial patterning of Arabidopsis roots. In hybrid poplar ( P. tremula × P. alba clone INRA 717-1B4), PtaSHR2 was preferentially expressed in axillary buds (AXBs) and transcriptionally up-regulated during AXB maturation and activation. Overexpression of SHR2 ( PtSHR2 OE ) induced an enhanced outgrowth of AXBs below the bud maturation point, with a simultaneous transition of an active shoot apex into an arrested terminal bud. The larger and more mature AXBs of PtSHR2 OE trees revealed altered expression of genes involved in axillary meristem initiation and bud activation, as well as a higher ratio of cytokinin to auxin. To elucidate the underlying mechanism of PtSHR2 OE -induced high branching, subsequent molecular and biochemical studies showed that compared with wild-type trees, decapitation induced a quicker bud outburst in PtSHR2 OE trees, which could be fully inhibited by exogenous application of auxin or cytokinin biosynthesis inhibitor, but not by N-1-naphthylphthalamic acid. Our results indicated that overexpression of PtSHR2B disturbed the internal hormonal balance in AXBs by interfering with the basipetal transport of auxin, rather than causing auxin biosynthesis deficiency or auxin insensitivity, thereby releasing mature AXBs from apical dominance and promoting their outgrowth.