Strigolactones Decrease Leaf Angle in Response to Nutrient Deficiencies in Rice

Abstract

Strigolactones (SLs) are a class of plant hormones that are synthesized from b-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 SLbiosynthesis 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.

Plant apocarotenoids: from retrograde signaling to interspecific communication

“…For instance, Arabidopsis, rice, and pea SL‐deficient and ‐insensitive mutants showed a higher degree of shoot branching/tillering than the wild type (Gomez‐Roldan et al ., 2008; Umehara et al ., 2008). Furthermore, SLs are involved in many other shoot‐related developmental processes such as regulation of rice tiller angle by attenuating shoot gravitropism (Sang et al ., 2014), promotion of shoot secondary growth, elongation of internodes (Agusti et al ., 2011; de Saint et al ., 2013), inhibition of hypocotyl and mesocotyl growth (Hu et al ., 2010; Tsuchiya et al ., 2010; Hu et al ., 2014; Jia et al ., 2014; Sun et al ., 2018; Wang et al ., 2020c), induction of leaf senescence (Snowden et al ., 2005; Yamada et al ., 2014) and decreasing the rice leaf angle in response to nutrient deficiencies (Sun et al ., 2014; Shindo et al ., 2020). They also play key roles in determining root architecture.…”

Synergistic Interaction of Phytohormones in Determining Leaf Angle in Crops

“…SLs negatively regulate leaf inclination at seedling stage [ 77 ]. Interestingly, recent report showed that SLs also mediated leaf inclination in response to nutrient deficiencies in rice [ 78 ]. Similar to SLs, JA also showed a negative role in leaf inclination.…”

Rapid analysis of strigolactone receptor activity in a Nicotiana benthamiana dwarf14 mutant

“…Strigolactones (SLs) are a family of plant hormones derived from β‐carotene that have diverse functions in plants (Bouwmeester et al, 2021 ; Machin et al, 2020 ; Waters et al, 2017 ). SLs regulate axillary bud outgrowth (tillering), stem elongation, auxin transport, root elongation, leaf shape, leaf angle, leaf senescence, cambial growth, susceptibility to pathogenic microbes and root‐knot nematodes, stomatal closure responses, and drought tolerance (Agusti et al, 2011 ; Bu et al, 2014 ; Gomez‐Roldan et al, 2008 ; Kalliola et al, 2020 ; Kapulnik et al, 2011 ; Lahari et al, 2019 ; Lauressergues et al, 2015 ; Li et al, 2017 , 2020 ; Marzec et al, 2016 ; Nasir et al, 2019 ; Ruyter‐Spira et al, 2011 ; Scaffidi et al, 2013 ; Shindo et al, 2020 ; Shinohara et al, 2013 ; Soundappan et al, 2015 ; Ueda & Kusaba, 2015 ; Umehara et al, 2008 ; Van Ha et al, 2014 ; Yamada et al, 2014 ). SLs are also exuded by roots into the rhizosphere, especially under nutrient‐poor conditions.…”