Abstract
Plants produce strigolactones (SLs) in roots in response to nitrogen or phosphate deficiency. To evaluate SL levels under other mineral deficiencies in rice, we cultivated rice seedlings in hydroponic media without nitrogen, phosphorus, potassium, sulfur, calcium, magnesium, and iron. Tiller bud outgrowth was stimulated under calcium deficiency because of low SL levels. SL levels increased under sulfur deficiency, in addition to phosphate, and nitrogen deficiencies. To explore which genes are key regulators of SL production under sulfur deficiency, we analyzed the expression of SL‐related genes in sulfur‐sufficient and sulfur‐deficient conditions. An SL biosynthesis gene, DWARF27 (D27), was strongly expressed under sulfur deficiency, and its expression was decreased by sulfur supply. The levels of D10, D17, and OsMAX1 transcripts did not differ between sulfur‐sufficient and sulfur‐deficient conditions. These results suggest that the increased SL levels under sulfur deficiency are due to a high expression of D27. A combination of nitrogen, phosphorus, and sulfur deficiencies had no additive synergistic effect on SL production. Under combined phosphorus and sulfur deficiency, the expression levels of most SL biosynthesis genes were elevated. The number of tiller buds in the d27 mutant was higher than in the wild type, but lower than in other d mutants. Under sulfur deficiency, the chlorophyll content of d27 was lower than those of other d mutants. These results indicate that D27 plays an important role in adaptation to sulfur deficiency in rice.
Highlights
Strigolactones (SLs) are a class of terpenoid lactones that were originally discovered as stimulants of seed germination in root parasitic plants such as Striga spp., Orobanche spp., and Phelipanche spp
We show that D27 is strongly expressed under S deficiency, and its expression is reduced by S supply, whereas the expression levels of D10, D17, and OsMAX1 are not affected by S supply
These results suggest that SL production under S deficiency is due to a marked increase in the expression of D27
Summary
Strigolactones (SLs) are a class of terpenoid lactones that were originally discovered as stimulants of seed germination in root parasitic plants such as Striga spp., Orobanche spp., and Phelipanche spp. (for reviews, see Xie, Yoneyama, & Yoneyama, 2010; Yoneyama, Awad, Xie, Yoneyama, & Takeuchi, 2010). Because SL-related mutants show pleiotropic phenotypes including enhanced shoot branching, SLs have recently been recognized as plant hormones that control plant growth at. Canonical SLs have tricyclic lactone and methylbutenolide moieties connected by an enol ether bond This bond and the methylbutenolide structure are essential for shoot branching inhibition (Boyer et al, 2012; Umehara et al, 2015). Several types of SLs have been identified; these are mainly produced in roots in response to P deficiency in various plant species including red clover, tomato, sorghum, Lotus japonicus, alfalfa, and rice (Lopez-Raez et al, 2008; Sugimoto & Ueyama, 2008; Umehara et al, 2008; Yoneyama, Xie, et al, 2007; Yoneyama, Yoneyama, Takeuchi, & Sekimoto, 2007; Yoneyama et al, 2012). Under P deficiency, SL levels in roots are highly elevated and SLs are probably transported to tiller buds to inhibit the outgrowth. Under S deficiency, tiller bud outgrowth in a d27 mutant was strongly suppressed compared with that in other d mutants, and chlorophyll content was lower than that in other d mutants, indicating that D27 expression plays an important role in survival and adaptation to S deficiency
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