Identification of molecular mechanisms associated with increased yield caused by mechanical treatment in Arabidopsis thaliana

RAMINGER, BETINA LORENA; CHAN, RAQUEL LÍA; CABELLO, JULIETA VIRGINIA

Mendoza

Congreso; LVIII Reunión SAIB; 2022

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

Arabidopsis thaliana genotypes that yield significantly more than others exhibit large stem diameters and an increased number of vascular bundles. These characteristics can be obtained by adding a 1.5 g hanging weight placed at the apex of a 4 cm height Arabidopsis floral rod for 48 h. The increase in the number of vascular bundles happens by duplication of the existing ones from the apex through the base, like auxin flow, similarly to branching from the floral stem. Auxin and its carriers are essential for the response to the hanging weight treatment and new bundle generation.To investigate the putative role of brassinosteroids (BS) in this process, we initially evaluated mutants in genes involved in the BS signaling pathways. Bes1 and bzr1 did not respond to the weight treatment, and in agreement, the exogenous addition of brassinazole (an inhibitor of BS biosynthesis) to WT plants interrupted the response.BCR1 is a negative regulator of branching and a positive regulator of the CLE44 peptide expression, which participates in the proliferation and differentiation of procambium cells. BCR1 is regulated by auxin, BS, and strigolactones (SL). The weight treatment on brc1, cle44, and max4 mutants did not cause any effect. The same scenario was observed when the sparsely branched ecotype of Arabidopsis, Zurich (Zu-0), was weight treated. In agreement, none of these genotypes increased seed production; on the contrary, CLE44 mutant showed a decrease in seed yield. The better performance showed by WT plants after weight treatment can be explained by an increase in photosynthates transport from source to sink tissues. The expression of genes encoding enzymes participating in starch synthesis and degradation, as well as sucrose transporters, was induced after treatment. In addition, treated plants had a higher concentration of lipids in seeds, while the opposite occurred in CLE44 mutants. Roots were also affected by weight treatment, increasing the primary root diameter and the number of vascular bundles, the total biomass, and the sucrose transport by phloem tissue.Altogether the results indicate that the weight treatment triggers a complex process involving AUX, BS, and SA phytohormones. Moreover, we can conclude that molecular mechanisms involving branching play a crucial role in this event, and CLE44 has a critical role in this response which needs further investigation