Plastidic transporter involved in the biosynthesis of aliphatic glucosinolates by translocating the biosynthetic intermediates of Met-derived glucosinolates across chloroplast membranes. Transports short chain (C2) alpha-keto acids, such as 4-methylsulfanyl-2-oxobutanoic acid, from the cytosol to the chloroplast where they are subjected to chain elongation cycles. Functions also in the transport of chain-elongated (C3 to C8) Met derivatives from the chloroplast to the cytosol. Does not seem to be involved in the transport of indole-derived glucosinolates. Widely expressed. By wounding and methyl jasmonate (MeJa). Down-regulated by salicylic acid (SA). No visible phenotype under normal growth conditions, but plants contain reduced levels of aliphatic glucosinolates. Belongs to the bile acid:sodium symporter (BASS) (TC 2.A.28) family.