Evolutionary and Gene Expression Analyses Reveal New Insights into the Role of <i>LSU</i> Gene-Family in Plant Responses to Sulfate-Deficiency

LSU (RESPONSE TO LOW SULFUR) proteins belong to a plant-specific gene family initially characterized by their strong induction in response to sulfate (S) deficiency. However, little is known about the LSU gene repertoire and evolution of this family in land plants. In this work, a total of 270 LSU family members were identified using 134 land plant species with whole genome sequence available. Phylogenetic analysis revealed that LSU genes belong to a Spermatophyta-specific gene family, and their homologs are distributed in three major groups, two for dicotyledons and one group for monocotyledons. Moreover, we analyzed the expression of LSU genes in one representative species of each phylogenetic group (wheat, tomato and Arabidopsis) and found a conserved response to S-deficiency, suggesting that these genes might play a key role in S stress responses. Accordingly, Arabidopsis lsu2 knockout mutant plants showed increased levels of internal sulfate content and lower levels of expression of different key genes involved in S deficiency and metabolism like SDI2 and APR3. In summary, our results indicate that LSU genes are evolutionarily conserved in angiosperms and that specific members of this family might play an important role regulation of S transport and assimilation.