Non‐dormant Axillary Bud 1 regulates axillary bud outgrowth in sorghum

Abstract

Tillering contributes to grain yield and plant architecture and therefore is an agronomically important trait in sorghum (Sorghum bicolor). Here, we identified and functionally characterized a mutant of the Nondormant Axillary Bud 1 (NAB1) gene from an ethyl methanesulfonate-mutagenized sorghum population. The nab1 mutants have increased tillering and reduced plant height. Map-based cloning revealed that NAB1 encodes a carotenoid-cleavage dioxygenase 7 (CCD7) orthologous to rice (Oryza sativa) HIGH-TILLERING DWARF1/ DWARF17 and Arabidopsis thaliana MORE AXILLARY BRANCHING 3. NAB1 is primarily expressed in axillary nodes and tiller bases and NAB1 localizes to chloroplasts. The nab1 mutation causes outgrowth of basal axillary buds; removing these non-dormant basal axillary buds restored the wild-type phenotype. The tillering of nab1 plants was completely suppressed by exogenous application of the synthetic strigolactone analog GR24. Moreover, the nab1 plants had no detectable strigolactones and displayed stronger polar auxin transport than wild-type plants. Finally, RNA-seq showed that the expression of genes involved in multiple processes, including auxin-related genes, was significantly altered in nab1. These results suggest that NAB1 functions in strigolactone biosynthesis and the regulation of shoot branching via an interaction with auxin transport.

Transcriptome analyses provide insights into the homeostatic regulation of axillary buds in upland cotton (G. hirsutum L.)

“…The axillary buds are an important agronomic trait that shapes plant structure, biomass and yield. In most higher plants, the branches originate from axillary meristems, while the main stem is derived from the apical meristems [1][2][3]. In different species, axillary buds show different degrees of development and growth during the vegetative period [4].…”

“…In rice (Oryza sativa), the growth of axillary buds is released to form tillers because of its characteristic growth habit [3], while in maize (Zea mays), another monocot species, the outgrowth of the axillary buds remains relatively restricted [8]. In sorghum (Sorghum bicolor), the Nondormant Axillary Bud 1 gene was identified from a mutant plant and functionally characterized, and the mutant showed an increase in tillers and reduced plant height [1].…”

Strigolactones inhibit auxin feedback on PIN-dependent auxin transport canalization

“…SLs represent a recently discovered class of plant growth regulators and their developmental roles and signaling mechanisms are not yet fully characterized. SLs have been shown to influence a range of plant traits including shoot branching 30,31 , shoot gravitropism 32 , secondary growth 33 , adventitious rooting 34 as well as lateral rooting and root hair elongation 35,36 . Many of the processes targeted by SLs also require auxin transport, specifically its canalization as proposed for the classical SL effect on shoot branching 37 .…”

Carotenoid Cleavage Dioxygenase Genes of Chimonanthus praecox, CpCCD7 and CpCCD8, Regulate Shoot Branching in Arabidopsis

“…For example, among eudicots including of Arabidopsis, pea, petunia and tomato, the MAX3, RMS5, PhCCD7 and SlCCD7 genes are mainly expressed in roots and stems, and the expression level of Arabidopsis MAX3 is 2-fold higher in roots than in stems [15,20,51]. Among monocots, the Non-dormant Axillary Bud 1 (NAB1) gene of sorghum shows the highest expression level in nodes, followed by stems, roots and young panicles [53]; the high tillering dwarf 1 (htd1) gene of rice shows strong expression in stems, and the lowest expression level in roots [54]; ZmCCD7/ZpCCD7 of maize (Zea mays) is strongly expressed in roots [27]. Among the CCD homologs of perennial woody plants, PtrMAX3 of poplar (Populus trichocarpa) [55], AcCCD7 of kiwifruit (Actinidia chinensis) [2] and MdCCD7 of apple [50] show the highest expression in roots.…”