CONNECTIONS BETWEEN OXR PROTEINS AND THE CYTOKININ PATHWAY IN ARABIDOPSIS

EUSEBI, DELFINA; MENCIA, REGINA; WELCHEN, ELINA

Congreso; LVIII Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology Research; 2022

Our group aims to identify new proteins involved in defense mechanisms against oxidative stress in Arabidopsis thaliana. Plants over-expressing AtOXR2 (oeOXR2) exhibited interesting phenotype characteristics like a larger size, higher biomass and increased resistance to hemibiotrophic pathogens infection compared to WT plants. These characteristics could result from higher Cytokinins (CKs) content or differences in sensitivity and signaling pathways. Using a GFP-reporter, we observed that oeOXR2 plants showed increased CK levels while the T-DNA knockout mutant (oxr2) presented a decreased accumulation of CKs compared with de WT (Col-0) plants. In agreement, the root development of oeOXR2 plants coincides with those of plants with higher CK levels. Therefore, we focused on this plant organ to analyze in depth the role of OXR proteins in the metabolism and CKs signalling pathway. oeOXR2 plants were less sensitive to the addition of the exogenous BAP (6-Benzylaminopurine) since they showed a significant increase in primary root length (17 mm vs 14 mm) and a larger rosette area (10 mm2 vs five mm2) compared to 7-day WT plants grown in the presence of at 50 nM BAP. In contrast, under the same conditions, the oxr2 mutant develops shorter roots (12 mm) and significantly reduced rosette area (2.5 mm2). Furthermore, we obtained plants with increased expression of AtOXR2 in the background of ahp1/2/3/4 quadruple and arr3/4/5/6/8/9 sextuplet mutants and made crosses between oeOXR2 and ahk4 mutants and over-expressing plants in the CK oxidases (oeCKX). Higher expression of AtOXR2 failed to reverse the root phenotype of the ahp and arr mutants both in control and at 25 nM BAP levels. However, it partially reverses the root phenotype of oeCKX plants. We propose that the accumulation of the hormone and the stimulated response to it could be the response to a partial inhibition of the catalytic activity of CKXs enzymes in the redox-modified environment of oeOXR2 plants.