Amino Acid Transporter Genes Are Essential for <em>FLO11</em>-Dependent and <em>FLO11</em>-Independent Biofilm Formation and Invasive Growth in <em>Saccharomyces cerevisiae</em>

<div><p>Amino acids can induce yeast cell adhesion but how amino acids are sensed and signal the modulation of the <em>FLO</em> adhesion genes is not clear. We discovered that the budding yeast <em>Saccharomyces cerevisiae</em> CEN.PK evolved invasive growth ability under prolonged nitrogen limitation. Such invasive mutants were used to identify amino acid transporters as regulators of <em>FLO11</em> and invasive growth. One invasive mutant had elevated levels of <em>FLO11</em> mRNA and a Q320STOP mutation in the <em>SFL1</em> gene that encodes a protein kinase A pathway regulated repressor of <em>FLO11</em>. Glutamine-transporter genes <em>DIP5</em> and <em>GNP1</em> were essential for <em>FLO11</em> expression, invasive growth and biofilm formation in this mutant. Invasive growth relied on known regulators of <em>FLO11</em> and the Ssy1-Ptr3-Ssy5 complex that controls <em>DIP5</em> and <em>GNP1</em>, suggesting that Dip5 and Gnp1 operates downstream of the Ssy1-Ptr3-Ssy5 complex for regulation of <em>FLO11</em> expression in a protein kinase A dependent manner. The role of Dip5 and Gnp1 appears to be conserved in the <em>S. cerevisiae</em> strain ∑1278b since the <em>dip5 gnp1</em> ∑1278b mutant showed no invasive phenotype.</p> <p>Secondly, the amino acid transporter gene <em>GAP1</em> was found to influence invasive growth through <em>FLO11</em> as well as other <em>FLO</em> genes. Cells carrying a dominant loss-of-function <em>PTR3^{647::CWNKNPLSSIN}</em> allele had increased transcription of the adhesion genes <em>FLO1, 5</em>, <em>9</em>, <em>10</em>, <em>11</em> and the amino acid transporter gene <em>GAP1</em>. Deletion of <em>GAP1</em> caused loss of <em>FLO11</em> expression and invasive growth. However, deletions of <em>FLO11</em> and genes encoding components of the mitogen-activated protein kinase pathway or the protein kinase A pathway were not sufficient to abolish invasive growth, suggesting involvement of other <em>FLO</em> genes and alternative pathways. Increased intracellular amino acid pools in the <em>PTR3^{647::CWNKNPLSSIN}</em>-containing strain opens the possibility that Gap1 regulates the <em>FLO</em> genes through alteration of the amino acid pool sizes.</p>