Involved in plant growth and salt and osmotic tolerance. Catalyzes the decarboxylation of 4'-phosphopantothenoylcysteine to 4'-phosphopantetheine, a key step in coenzyme A biosynthesis. The enzyme is also able to decarboxylate pantothenoylcysteine to pantothenoylcysteamine. H(+) + N-[(R)-4-phosphopantothenoyl]-L-cysteine = (R)-4'-phosphopantetheine + CO2 Binds 1 FMN per subunit. Cofactor biosynthesis; coenzyme A biosynthesis; CoA from (R)-pantothenate: step 3/5. Homotrimer. Expressed in roots, shoots, leaves, flowers, developing siliques and seeds. By salt stress. No visible phenotype under normal growth conditions, but homozygous double mutants hal3a-1 and hal3b are embryonic lethal. Belongs to the HFCD (homooligomeric flavin containing Cys decarboxylase) superfamily. Was previously called At1g48610. The predicted gene At1g48610 has been split into 2 genes: At1g48605 and At1g48610.