Azospirillum brasilense modifies Arabidopsis root architecture through indole acetic acid-dependent and independent mechanisms

LOPEZ, GASTON; DONADIO, FLORENCIA; CASSAN, FABRICIO; MOLINA, ROMINA; NIEVAS, SOFÍA; MORA, VERÓNICA; CONIGLIO, ANAHI; TORRES, DANIELA

Congreso; XXX REUNION LATINOAMERICANA DE RIZOBIOLOGIA, V CONFERENCIA LATINOAMERICANA DE MICROORGANISMOS PROMOTORES DEL CRECIMIENTO VEGETAL; 2021

RELAR

Azospirillum is one of the most studied genus of plant growth promotingrhizobacteria (pgpr). The positive effects of A. brasilense on plants havebeen mostly, but not exclusively, explained by the bacterial production of thephytohormone indole-3-acetic acid (IAA). The main objective of our study was toevaluate the role of the bacterial iaa as co-responsible of changes observed inmorphology and architecture roots of Arabidopsis thaliana and to evaluate thenature of a putative IAA-independent mechanism. The root architecture of A.thaliana was evaluated after inoculation with A. brasilense Az39, other bacteria orthe treatment with exogenous iaa. Seeds of A. thaliana Col-0 or its mutant tir 1.1were germinated vertically in Petri dishes containing ms medium for 7 d (photoperiod16/8h, 22 ºC). Seedlings were then aseptically transferred to MS plates containing108 cfu·ml-1 of Az39; the heat inactivated cells of this strain (Az39φ); theIAA-deficient mutant (Az39ΔipdC); or E. coli DH5α, as negative control. After 5 dpost-transplantation, the root architecture was evaluated using an image analysissystem. Our results demonstrate the ability of Az39 to modify the primary rootdevelopment through iaa biosynthesis, while other IAA-independent mechanismswere related to an increase in the lateral roots development and the root hairsnumber. The physical presence of the inactive bacteria (Az39φ) seems to mediatethe development of root hairs, a mechanism common to other non-pgpr as E. coliDH5α. Our results suggest that Az39 inoculation induces morphological changesin root architecture through both IAA-independent and dependent mechanism.The iaa biosynthesis by Az39 reduces the primary root length; while the cellscontact with the roots increases the root hairs production. Both the synthesis ofactive iaa and the presence of metabolically active Az39 cells increase the growthand development of lateral roots.