Light is one of the environmental signals that regulate axillary shoot development.
However, little is known about molecular and physiological mechanisms regulating the
development of the axillary shoot in response to light signals. Molecular events
associated with the enhanced apical dominance of phytochrome B mutant sorghum
(Sorghum bicolor) were analyzed to reveal processes mediating axillary shoot
development in response to light. The enhanced apical dominance of phyB-1 mutant
sorghum is due to inhibition of bud outgrowth and is accompanied by upregulation of
the dormancy-associated gene (SbDRM1) in the buds. Increased expression of the
Teosinte Branched1 (SbTB1) gene (encoding a putative transcription factor that
represses bud outgrowth) suggests that the inhibition of bud outgrowth in phyB-1
sorghum is due to the absence of active phyB to repress SbTB1. The results were
confirmed by growing wild type seedlings at high plant density or with supplemental farred
(FR) light that induces enhanced apical dominance. However, the SbTB1 gene is not
involved in the inhibition of bud outgrowth induced by defoliation in wild type seedlings. The results indicate variations in molecular mechanisms among different
signals inhibiting branching. Increased expression of SbMAX2 (which encodes an F-box
protein that represses bud outgrowth) in buds repressed by light and defoliation suggests
common mechanisms at the downstream end of pathways inhibiting branching.
The expression levels of several cell cycle-related genes including SbPCNA, SbHis4,
SbCycD2, SbCycB and SbCDKB were down-regulated in the repressed buds of FRtreated
and defoliated seedlings indicating the suspension of cell division in those buds.
However, these cell cycle-related genes were continuously expressed in the repressed
buds of phyB-1, suggesting that inhibition of bud outgrowth in phyB-1 is not associated
with down-regulation of cell cycle-related gene expression. The down-regulation of cell
cycle-related genes in the buds of FR-treated wild type seedlings indicates that other
sensors, in addition to phyB, regulate bud outgrowth in response to FR enrichment. The
approaches used and results achieved will provide direction for future research on this
important topic.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1668 |
| Date | 15 May 2009 |
| Creators | Kebrom, Tesfamichael Hintsa |
| Contributors | Finlayson, Scott A, Mullet, John E |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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