SPL14/17 act downstream of strigolactone signalling to modulate rice root elongation in response to nitrate supply
2021
Sun, Huwei | Guo, Xiaoli | Qi, Xuejiao | Feng, Fan | Xie, Xiaonan | Zhang, Yali | Zhao, Quanzhi
Nitrogen (N) is an essential major nutrient for food crops. Although ammonium (NH₄⁺) is the primary N source of rice (Oryza sativa), nitrate (NO₃⁻) can also be absorbed and utilized. Rice responds to NO₃⁻ application by altering its root morphology, such as root elongation. Strigolactones (SLs) are important modulators of root length. However, the roles of SLs and their downstream genes in NO₃⁻‐induced root elongation remain unclear. Here, the levels of total N and SL (4‐deoxyorobanchol) and the responses of seminal root (SR) lengths to NH₄⁺ and NO₃⁻ were investigated in rice plants. NO₃⁻ promoted SR elongation, possibly due to short‐term signal perception and long‐term nutrient function. Compared with NH₄⁺ conditions, higher SL signalling/levels and less D53 protein were recorded in roots of NO₃⁻‐treated rice plants. In contrast to wild‐type plants, SR lengths of d mutants were less responsive to NO₃⁻ conditions, and application of rac‐GR24 (SL analogue) restored SR length in d10 (SL biosynthesis mutant) but not in d3, d14, and d53 (SL‐responsive mutants), suggesting that higher SL signalling/levels participate in NO₃⁻‐induced root elongation. D53 interacted with SPL17 and inhibited SPL17‐mediated transactivation from the PIN1b promoter. Mutation of SPL14/17 and PIN1b caused insensitivity of the root elongation response to NO₃⁻ and rac‐GR24 applications. Therefore, we conclude that perception of SLs by D14 leads to degradation of D53 via the proteasome system, which releases the suppression of SPL14/17‐modulated transcription of PIN1b, resulting in root elongation under NO₃⁻ supply.
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