SPL14/17 act downstream of strigolactone signalling to modulate rice root elongation in response to nitrate supply

• Published in: The Plant journal : for cell and molecular biology Vol. 106; no. 3; pp. 649 - 660
• Main Authors: Sun, Huwei, Guo, Xiaoli, Qi, Xuejiao, Feng, Fan, Xie, Xiaonan, Zhang, Yali, Zhao, Quanzhi
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.05.2021
• Subjects: Ammonium; Biosynthesis; Elongation; Modulators; Morphology; Mutants; Mutation; nitrate (NO3−); Nitrates; Nitrogen; Nutrients; Oryza sativa; Perception; Proteasomes; protein interaction; Rice; seminal root (SR); Signaling; strigolactones (SLs); Transcription; nitrate (NO3−); strigolactones (SLs); protein interaction; rice; seminal root (SR)
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.15188

SUMMARY 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. Significance Statement Under NH4+ treatment, D53 protein binds to SPL14/17, repressing their transcriptional activities and inhibiting root elongation in rice (Oryza sativa). Under NO3− conditions, the perception of SLs by D14 results in degradation of D53 via the proteasome system, which stops the suppression of SPL14/17‐mediated transcription of PIN1b and leads to root elongation in rice.