Strigolactones Are Involved in Root Response to Low Phosphate Conditions in Arabidopsis  

Abstract

Strigolactones (SLs) are plant hormones that suppress lateral shoot branching, and act to regulate root hair elongation and lateral root formation. Here, we show that SLs are regulators of plant perception of or response to low inorganic phosphate (Pi) conditions. This regulation is mediated by MORE AXILLARY GROWTH2 (MAX2) and correlated with transcriptional induction of the auxin receptor TRANSPORT INHIBITOR RESPONSE1 (TIR1). Mutants of SL signaling (max2-1) or biosynthesis (max4-1) showed reduced response to low Pi conditions relative to the wild type. In max4-1, but not max2-1, the reduction in response to low Pi was compensated by the application of a synthetic strigolactone GR24. Moreover, AbamineSG, which decreases SL levels in plants, reduced the response to low Pi in the wild type, but not in SL-signaling or biosynthesis mutants. In accordance with the reduced response of max2-1 to low Pi relative to the wild type, several phosphate-starvation response and phosphate-transporter genes displayed reduced induction in max2-1, even though Pi content in max2-1 and the wild type were similar. Auxin, but not ethylene, was sufficient to compensate for the reduced max2-1 response to low Pi conditions. Moreover, the expression level of TIR1 was induced under low Pi conditions in the wild type, but not in max2-1. Accordingly, the tir1-1 mutant showed a transient reduction in root hair density in comparison with the wild type under low Pi conditions. Therefore, we suggest that the response of plants to low Pi is regulated by SLs; this regulation is transmitted via the MAX2 component of SL signaling and is correlated with transcriptional induction of the TIR1 auxin receptor.

Strigolactones fine-tune the root system

“…However, little has been reported on the effect of nutrient deficiency and root hair length, which seems to be the aspect of root hair development most affected by strigolactones. However, it has been suggested that the root hair response to low Pi is mediated by strigolactones and could be correlated with transcriptional activation of TIR1, thus complementing the experimental evidence that auxin is sufficient to compensate for the reduced max2 responses (Mayzlish-Gati et al 2012). …”

“…In contrast to lateral root formation, Pi-deficient inhibition of root growth occurs independently of strigolactone signaling, as evidenced by Pi-deficient inhibition of primary root growth in both max2 and wild type (Yoneyama et al 2007;Jain et al 2007;Mayzlish-Gati et al 2012).…”

The role of strigolactones in root development

“…Moreover, abamineSG, which decreases SL levels in plants, reduced the response to low P in wild-type, but not in SL mutant, plants. 22 Interestingly, several lines of evidence suggest that SLs are involved in rice root growth in response to N and P deficiencies. 3,4 The application of GR24 to wild-type plants and SL synthetic mutants, but not signaling mutants (d3), under nutrientsufficient conditions led to the complete recovery of seminal root length and LR density compared to wild-type plants under Nand P-deficient conditions.…”

“…14,[16][17][18][19][20][21] Recently, it was reported that SLs regulate the perception or response of plants to P-limited conditions. 22 In Arabidopsis, mutants of SL signaling (max2-1) and biosynthesis (max4-1) showed reduced responses to P-limited conditions relative to wild-type plants. In max4-1, but not max2-1, the reduced response to low P was compensated by GR24 application.…”

“…4,7,9,22 SLs may affect root growth via changes in auxin polar transport from shoot to root and/or auxin efflux in roots. Exogenous supplementation with GR24 interfered with PIN auxinefflux carriers in roots, 4 reducing the PIN1-GFP intensity in LR primordial.…”