Turanose induced WOX5 restores symbiosis in the Medicago truncatula cytokinin perception mutant cre1

Abstract

Rhizobia-legume interaction recruits cytokinin for the induction of nodule primordia in the cortex. In Medicago truncatula, cytokinin signalling involves flavonoid mediated local alteration of polar auxin transport for triggering cortical cell division. Since sugar signalling is widely evidenced to trigger auxin responses, we explored whether sugar treatment could compensate for cytokinin signalling in M. truncatula cytokinin perception mutant cre1. Herein we demonstrate that turanose, a non-metabolizable sucrose analogue can trigger auxin response and show signs of recovery of symbiosis in cre1. Additionally, turanose upregulated the expression of WUSCHEL-related homeobox 5 (MtWOX5) which prompted us to check if overexpression of WOX5 could rescue cre1. Intriguingly, while overexpression of MtWOX5 failed, WOX5 from Arachis hypogaea (AhWOX5) completely restored functional symbiosis in cre1 with an efficiency resembling the wildtype. This indicate that indeterminate and determinate WOX5 responds to differential cues for nodule development and is consistent with their distinct clustering in distance trees. The mechanism of compensation of cytokinin signalling for recovery of symbiosis in cre1 was distinct for turanose treatment and AhWOX5 expression. Turanose increased MtHK2 level by ∼5-fold and doubled the level of MtRR4 whereas AhWOX5 elevated the level of MtRR4 by ∼12-fold without affecting the level of MtHK2/3. Thus, turanose compensated MtCRE1 at receptor level whereas WOX5 restored the signalling at the level of response regulators. We propose a working model to discuss how sugar mediated WOX5 signalling have compensated MtCRE1 to recover normal progress of symbiosis in cre1.One sentence summarySugar signalling rescues symbiosis in Medicago truncatula cytokinin perception mutant cre1