Azospirillum brasilense modifies Arabidopsis root architecture through indoleacetic acid-dependent and independent mechanisms.

MORA, VERÓNICA; LÓPEZ, GASTÓN; MOLINA, ROMINA; CONIGLIO, ANAHÍ; DONADIO, FLORENCIA; NIEVAS, SOFÍA; CASSÁN, FABRICIO

Montevideo

Congreso; XXX Reunión Latinoamericana de Rizobiología. V Conferencia Latinoamericana de Microorganismos Promotores del Crecimiento Vegetal.; 2021

Asociación Latinoamericana de Rizobiología (ALAR)

Azospirillum is one of themost studied genus of plant growth promoting rhizobacteria (PGPR). The positiveeffects 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 Arabidopsisthaliana and to evaluate the nature of a putative IAA-independentmechanism. The root architecture of A.thaliana was evaluated after inoculation with A. brasilense Az39, other bacteria or the treatment with exogenousIAA. Seeds of A. thaliana Col-0 orits mutant tir 1.1 were germinatedvertically in Petri dishes containing MS medium for 7 d (photoperiod 16/8h, 22ºC). Seedlings were then aseptically transferred to MS plates containing 108cfu·ml-1 of Az39; the heat inactivated cells of this strain (Az39φ);the IAA-deficient mutant (Az39∆ipdC);or E. coli DH5α, as negative control.After 5 d post-transplantation, the root architecture was evaluated using animage analysis system. Our results demonstrate the ability of Az39 to modifythe primary root development through IAA biosynthesis, while otherIAA-independent mechanisms were related to an increase in the lateral roots developmentand the root hairs number. The physical presence of the inactive bacteria(Az39φ) seems to mediate the development of root hairs, a mechanism common toother non-PGPR as E. coli DH5α. Ourresults suggest that Az39 inoculation induces morphological changes in rootarchitecture through both IAA-independent and dependent mechanism. The IAAbiosynthesis by Az39 reduces the primary root length; while the cells contact withthe roots increases the root hairs production. Both the synthesis of active IAAand the presence of metabolically active Az39 cells increase the growth anddevelopment of lateral roots.