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

Abstract

Rhizobia-legume interaction recruits cytokinin-signaling that causes local auxin accumulation for the induction of nodule primordia in the cortex. Since sugar signaling can trigger auxin responses and regulate developmental processes, we explored whether sugar treatments could rescue cre1. Here we demonstrate that turanose, a non-metabolizable sucrose analogue can recover functional symbiosis in cytokinin perception mutant cre1. Additionally, turanose significantly upregulated the expression of WUSCHEL-related homeobox 5 (MtWOX5) which prompted us to check if ectopic expression of WOX5 could rescue cre1. Overexpression of WOX5 from Arachis hypogaea (AhWOX5), but not the intrinsic MtWOX5 could completely restore functional symbiosis in cre1 though both WOX5 (Mt and Ah) were functionally equivalent in inducing the expression of cytokinin inducible transcription factor Nodule Inception (NIN). Among the tested markers for cytokinin and auxin responses, significant differences were noted in the expression of IAA-Ala Resistant3 (MtIAR33), an auxin conjugate hydrolase. Turanose and AhWOX5 overexpression resulted in upregulation of MtIAR33 that further increased significantly in presence of rhizobia. On the other hand, MtIAR33 expression was unaffected in MtWOX5 overexpressed roots suggesting deconjugation driven auxin pool to be critical for rescuing symbiosis in cre1. We hypothesize a working model for sugar and WOX5 mediated rescue of symbiosis in cre1. One sentence summaryActivation of sugar-WOX5 signaling axis restores root nodule symbiosis in cytokinin perception mutant cre1