MtGRF8
interacts with
MtSymCRK
and prevents early bacteroid death during
Medicago
–
Sinorhizobium<
Chaoyan Yin, Kévin Magne, Fathi Berrabah, Dario Monachello, Gautier Bernal, Kirankumar S. Mysore, Jiangqi Wen, Catherine Etchebest, Pascal Ratet, Véronique Gruber Summary
In
Medicago littoralis R‐108
,
Symbiotic CYSTEINE‐RICH RECEPTOR‐LIKE KINASE
(
MtSymCRK
) is required to prevent defense reactions in symbiotic nodules during chronic infection.
MtSymCRK
represents a key legume symbiotic gene controlling nodule immunity and early bacteroid survival, but its mode of action in the cell signaling remains poorly understood.
This study investigated proteins interacting with MtSymCRK by screening an
Arabidopsis thaliana
open reading frame (ORF) library using yeast‐two‐hybrid followed by translational genetics towards R‐108. Finally, we conducted a reverse genetic approach in R‐108 using
Transposon of Nicotiana tabacum 1
(
Tnt1
) insertional mutants.
We identified a 14‐3‐3 protein, AtGENERAL REGULATORY FACTOR 8 (AtGRF8) interacting with MtSymCRK kinase domain (MtSymCRK
KIN
) and confirmed the interaction between MtSymCRK
KIN
and MtGRF8, the closest homolog of AtGRF8 in R‐108. Moreover, other members of the 14‐3‐3 family interact with MtSymCRK
KIN
but with a lower affinity than MtGRF8. We also demonstrated that the corresponding
Tnt1
mutant line
Mtgrf8
displays symbiotic dysfunctions in defense and senescence responses, resulting in a reduction of bacteroid differentiation. These dysfunctions compromise the intracellular survival of the rhizobia, thereby impairing the nitrogen fixation of rhizobia.
Our findings show that MtGRF8 and MtSymCRK are required for effective functioning of symbiosis and prevention of bacteroid death.