Abstract
Strigolactones (SLs) are a class of plant hormones that are synthesized from β-carotene through sequential reactions catalyzed by DWARF (D) 27, D17, D10, and OsMORE AXILLARY GROWTH (MAX) 1 in rice (Oryza sativa L.). In rice, endogenous SL levels increase in response to deficiency of nitrogen, phosphate, or sulfate (−N, −P, or −S). Rice SL mutants show increased lamina joint (LJ) angle as well as dwarfism, delayed leaf senescence, and enhanced shoot branching. The LJ angle is an important trait that determines plant architecture. To evaluate the effect of endogenous SLs on LJ angle in rice, we measured LJ angle and analyzed the expression of SL-biosynthesis genes under macronutrient deficiencies. In the “Shiokari” background, LJ angle was significantly larger in SL mutants than in the wild-type (WT). In WT and SL-biosynthesis mutants, direct treatment with the SL synthetic analog GR24 decreased the LJ angle. In WT, deficiency of N, P, or S, but not of K, Ca, Mg, or Fe decreased LJ angle. In SL mutants, deficiency of N, P, or S had no such effect. We analyzed the time course of SL-related gene expression in the LJ of WT deficient in N, P, or S, and found that expression of SL-biosynthesis genes increased 2 or 3 days after the onset of deficiency. Expression levels of both the SL-biosynthesis and signaling genes was particularly strongly increased under −P. Rice cultivars “Nipponbare”, “Norin 8”, and “Kasalath” had larger LJ angle than “Shiokari”, interestingly with no significant differences between WT and SL mutants. In “Nipponbare”, endogenous SL levels increased and the LJ angle was decreased under −N and −P. These results indicate that SL levels increased in response to nutrient deficiencies, and that elevated endogenous SLs might negatively regulate leaf angle in rice.
Highlights
Leaf angle is generally defined as the inclination between the leaf blade midrib and the stem, and is one of the most important plant architecture parameters that influence light interception, photosynthetic efficiency, and planting density (Mantilla-Perez and Salas Fernandez, 2017)
To simplify the comparison between WT and SL mutants, we focused on the 2nd lamina joint (LJ) angle
In a previous study (Li et al, 2014), the LJ angle was greater in d3-1 than in other d mutants, but in our experimental conditions, it was smaller in d3-1 (Figure 2B)
Summary
Leaf angle is generally defined as the inclination between the leaf blade midrib and the stem, and is one of the most important plant architecture parameters that influence light interception, photosynthetic efficiency, and planting density (Mantilla-Perez and Salas Fernandez, 2017). Rice LJ angle is regulated by plant hormones. Brassinosteroids (BR) stimulate elongation of adaxial parenchyma cells at the LJ and increase LJ angle (Wada et al, 1981; Cao and Chen, 1995; Zhang et al, 2009). Gibberellin stimulates cell elongation, and interacts with BR signaling by several regulators (Shimada et al, 2006; Wang et al, 2009). Gibberellin reduced the leaf angle by inhibiting BR response, demonstrating that gibberellin is a negative regulator of lamina inclination (Tong et al, 2014). Methyl jasmonate represses BR biosynthesis and signaling, and reduces LJ angle (Gan et al, 2015). How LJ angle is regulated by SL signal remains unknown
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
