Photosynthetic leaf area modulates tiller bud outgrowth in sorghum

Abstract

Shoot branches or tillers develop from axillary buds. The dormancy versus outgrowth fates of buds depends on genetic, environmental and hormonal signals. Defoliation inhibits bud outgrowth indicating the role of leaf-derived metabolic factors such as sucrose in bud outgrowth. In this study, the sensitivity of bud outgrowth to selective defoliation was investigated. At 6 d after planting (6 DAP), the first two leaves of sorghum were fully expanded and the third was partially emerged. Therefore, the leaves were selectively defoliated at 6 DAP and the length of the bud in the first leaf axil was measured at 8 DAP. Bud outgrowth was inhibited by defoliation of only 2 cm from the tip of the second leaf blade. The expression of dormancy and sucrose-starvation marker genes was up-regulated and cell cycle and sucrose-inducible genes was down-regulated during the first 24 h postdefoliation of the second leaf. At 48 h, the expression of these genes was similar to controls as the defoliated plant recovers. Our results demonstrate that small changes in photosynthetic leaf area affect the propensity of tiller buds for outgrowth. Therefore, variation in leaf area and photosynthetic activity should be included when integrating sucrose into models of shoot branching.

Transcriptome Profiling of Tiller Buds Provides New Insights into PhyB Regulation of Tillering and Indeterminate Growth in Sorghum

“…Expression of ASN1 is increased in buds of tiller inhibition tin mutant wheat and defoliated wild-type sorghum plants (Kebrom et al, 2012;Kebrom and Mullet, 2014). ASN1 expression is also elevated in darkness under conditions of low sugar status (Fujiki et al, 2001).…”

“…Sugar also stimulates bud outgrowth in pea and rose Mason et al, 2014;Barbier et al, 2015b). The expression of the Suc-starvation-inducible Gln-dependent Asn synthase (ASN) gene was increased and Suc-inducible PFP-gene encoding pyrophosphate-Fru-6-phosphate 1-phosphotransferase was down-regulated in dormant buds of tin in wheat and in buds repressed by defoliation in sorghum (Kebrom et al, 2012;Kebrom and Mullet, 2014). The molecular mechanism regulating Suc levels, and the specific signaling pathways mediating sugar sensing in buds, remain to be discovered (Barbier et al, 2015a).…”

“…The dormancy-versus-growth fates of axillary buds in diverse species have been linked to the level of Suc/ sugar-signaling and to changes in the expression of Sucresponsive genes in buds (Kebrom et al, 2012;Rabot et al, 2012;Kebrom and Mullet, 2014;Mason et al, 2014). Sugar signaling occurs through pathways involving hexokinase, trehalose-6-phosphate/SnRK1, and TOR, and by direct effects of sugars on growth and metabolism (Rolland et al, 2006;Lunn et al, 2014;Ruan, 2014).…”

“…The primers for sorghum ortholog of tb1 (SbTB1), SbMAX2, SbDRM1, SbPCNA, SbCycD2, SbCycB, and 18S rRNA used for qRT-PCR were published in Kebrom et al (2010). The primers for SbGT1 were published by Whipple et al (2011) and those for SbASN1 and SbPFP were published by Kebrom and Mullet (2014).…”

Cytokinins Are Initial Targets of Light in the Control of Bud Outgrowth

“…Decapitation aimed to release the axillary bud just below the stem section from apical dominance. Defoliation aimed to remove any correlative interactions between the axillary bud and its corresponding leaf, which were shown to modulate the bud's capacity to grow out (Le Hir et al, 2006;Girault et al, 2008;Ferguson and Beveridge, 2009;Kebrom et al, 2010;Kebrom and Mullet, 2015). As shown previously, defoliation does not impair bud outgrowth (Girault et al, 2008).…”