Abstract
Chrysanthemum (Dendranthema grandiflorum cv. Jinba) shoot branching is determined by bud outgrowth during the vegetative growth stage. The degree of axillary bud outgrowth is highly influenced by environmental conditions, such as nutrient availability. Here, we demonstrated that phosphorus (Pi) starvation significantly reduces axillary bud outgrowth in chrysanthemum. A strigolactone (SL) biosynthesis gene, DgCCD7, was isolated and characterized as an ortholog of MAX3/DAD3/RMS5/D17. By using ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS), three putative SLs were identified and levels of all three SLs showed strong increase under Pi starvation conditions. Determinations of the distribution of SLs and regulation of DgCCD7/8 in response to Pi changes in root indicate that SL acts systemically. However, temporal expression patterns of biosynthesis and signaling genes in nodes revealed that Pi starvation causes a local response of SL pathway. Treatment of node segments with or without auxin and Pi revealed that in the absence of exogenous auxin, Pi delayed axillary buds outgrowth and up-regulated local SL pathway genes. These data indicated that an auxin-SL regulatory loop responded to Pi starvation for delaying bud outgrowth locally, root biosynthesized SLs were transported acropetally and functioned in shoot branching inhibition under Pi starvation. We proposed that SLs contributed to chrysanthemum shoot branching control in response to Pi-limiting conditions in a systemic way.
Highlights
Shoot branching plays an important role in establishing plant architecture during development and growth, and confers flexibility of response to environmental stress in plants
Pi Starvation Causes Branching Reduction and indole acetic acid (IAA) Relocation in Chrysanthemum We used hydroponically grown plantlets taken from cuttings and tested them under different Pi treatments
A similar pattern was observed under Pi starvation culture conditions, indicating that distance to the top of the plant is one of the factors influencing bud outgrowth in chrysanthemum, at least for top 11 buds in this case
Summary
Shoot branching plays an important role in establishing plant architecture during development and growth, and confers flexibility of response to environmental stress in plants. Shoot branching is directly associated with ornamental value and industrial economics. Jinba) is one of the major cut flowers cultivated for domestic use worldwide. In China, Japan and Korea, standard commercial. Branching control by phosphate starvation cut chrysanthemums are required to bear a large flower on each stem. Manual pinching or removal of lateral buds and branches is a necessary procedure during the vegetative growth stage, which comprises one-third of the production cost. Clarification of the mechanisms underlying shoot branching, and effective approaches to control the process are essential for both breeders and farmers
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