The monomeric GTPases ArfA1 and RabA2 act in polar growth and bacterial infection during legume-rhizobia symbiosis

DALLA VIA, VIRGINIA; TRAUBENIK, SOLEDAD; RIVERO, CLAUDIO; ZANETTI, MARÍA EUGENIA; BLANCO, FLAVIO

Iguazú

Congreso; Internationl Molecular Plant Biolgy; 2015

Monomeric GTPases are molecular switches that regulate vesicle trafficking and cytoskeleton rearrangements. Previously, we have shown that RabA2a is involved in polar growth and early nodulation responses. RabA2a is corregulated with a GTPase of the ArfA1 subfamily. Both proteins co-localize in mobile vesicles in growing root hairs and in the infection thread, the channel that conducts rhizobia to the nitrogen-fixing organ called the nodule. ArfA1 is a subfamily integrated by several genes (5 in Medicago truncatula, 6 in both Phaseolus vulgaris and Arabidopsis thaliana) that encode almost identical proteins. Fusion of ArfA1 promoters to the GUS reporter gene showed expression in the root tip and root vascular tissue. Promoter of ArfA1a is active in root hairs, whereas ArfA1e is not. Both promoters showed activity in lateral roots and nodule primordia. Reverse genetics in M. truncatula and common bean (P. vulgaris) using mutated forms of ArfA1 revealed that this GTPase is required for root development and root hair growth. In the context of nodulation, expression of mutated forms of ArfA1 affected infection thread progression and the number of nodules in both legume species. Our results show that the same GTPases that are required for root and root hair growth have been recruited during evolution to mediate polar growth events associated to the rhizobia infection required for the establishment of the nitrogen-fixing symbiosis in legumes.