Abstract
Tillering in rice (Oryza sativa) is one of the most important agronomic traits that determine grain yields. Previous studies on rice tillering mutants have shown that the outgrowth of tiller buds in rice is regulated by a carotenoid-derived MAX/RMS/D (more axillary branching) pathway, which may be conserved in higher plants. Strigolactones, a group of terpenoid lactones, have been recently identified as products of the MAX/RMS/D pathway that inhibits axillary bud outgrowth. We report here the molecular genetic characterization of d27, a classic rice mutant exhibiting increased tillers and reduced plant height. D27 encodes a novel iron-containing protein that localizes in chloroplasts and is expressed mainly in vascular cells of shoots and roots. The phenotype of d27 is correlated with enhanced polar auxin transport. The phenotypes of the d27 d10 double mutant are similar to those of d10, a mutant defective in the ortholog of MAX4/RMS1 in rice. In addition, 2'-epi-5-deoxystrigol, an identified strigolactone in root exudates of rice seedlings, was undetectable in d27, and the phenotypes of d27 could be rescued by supplementation with GR24, a synthetic strigolactone analog. Our results demonstrate that D27 is involved in the MAX/RMS/D pathway, in which D27 acts as a new member participating in the biosynthesis of strigolactones.
Highlights
Shoot branching plays an important role in determining the diversity of plant architectures
By comparing the basipetal and acropetal IAA transport in uppermost internodes between the wild-type and d27 plants, we found that basipetal polar auxin transport (PAT) in d27 was significantly elevated, whereas acropetal PAT of 3H-IAA and basipetal transport of 3H-IAA treated with the PAT inhibitor N-1-naphthylphtalamic acid (NPA) showed no significant difference between the wild-type and mutant plants (Figure 5A)
Taraxacum officinale (To) investigate whether the increased auxin transport is related to the d27 mutant phenotype, we further examined the effect of NPA on d27 seedlings in hydroponic culture
Summary
Shoot branching plays an important role in determining the diversity of plant architectures. The outgrowth of axillary buds may be inhibited by the primary shoot, a phenomenon known as apical dominance (Sachs and Thimann, 1964; Cline, 1991). Indole-3-acetic acid (IAA) is the most abundant natural plant auxin and is synthesized mainly in the shoot apex and young leaves. It is transported along the shoot-root axis from cell to cell in a polar manner, which is essential for inhibiting the outgrowth of axillary buds (Ljung et al, 2001; Leyser, 2003; Sieberer and Leyser, 2006). It is plausible that auxin suppresses the outgrowth of axillary buds by influencing the supply of cytokinin to axillary buds
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