Soybean Ethylene Biosynthesis Genes Potentially Involved in Drought Tolerance

Soybean (Glycine max) is currently the most important source of edible oil and high-quality plant protein for feeding both human and animals worldwide. Considering the importance of this crop to Brazil, the second largest world soybean producer, it was created The Brazilian Soybean Genome Consortium (GENOSOJA). The project aims to investigate several aspects of soybean genomics, including gene and protein expression profile of soybean under biotic and abiotic stresses. Among all metabolic process that explain plant physiology, stands ethylene metabolism, a pathway widely studied in Arabidopsis thaliana, which triggers many molecular and cellular mechanisms, including stress response. This metabolic pathway starts a signal transduction network that culminates in synthesis of several transcription factors involved in gene activation/repression. Amongst the proteins that participated in ethylene biosynthesis, there is a key enzyme, 1-aminocyclopropane-1-carboxylate synthase (ACS) that converts S-adenosyl-methionine into 1-aminocyclopropane-1-carboxylate. ACS proteins in Arabidopsis thaliana can be divided into three main groups, based on their C-terminal sequences: type 1 proteins having extended C-terminal with conserved residues that are targets for phosphorylation by mitogen-activated protein kinase 6 (MAPK6), as well as a conserved residue that is a phosphorylation site for calcium-dependent protein kinase (CDPK); type 2 proteins having only CDPK sites; and type 3 proteins lacking both phosphorylation sites. Early molecular studies indicated that phosphorylation of ACS stabilized the protein and/or activated the enzyme. In the present work we found 21 ACS protein sequences in Glycine max databases, being seven type 1, five type 2 and nine type 3. The same analysis in A. thaliana and Oryza sativa databases show 11 and 6 proteins which represent ACS protein family, respectively (three type 1, five type 2 and three type 3 in A. thaliana; one type 1, one type 2 and four type 3 in O. sativa). Likewise were performed phylogenetic analysis of this gene family, followed by prediction of possible CDPK and MAPK6 phosphorylation sites in C-terminal of type 1 and 2 soybean ACS proteins. Thereby, nine out of twenty-one ACS soybean genes are identified as orthologous of A. thaliana and/or O. sativa ACS genes. In silico ACS expression analysis in soybean transcriptome, subjected to different stress conditions, revealed considerable expression levels only in 3 soybean ACC synthase (GmACS), under drought stress specifically, both classified as type 3. Our data suggest that ethylene biosynthesis is an important step in drought response and its further study will bring highlights to soybean stress response mechanisms.

Supported by EMBRAPA, CNPq, CAPES