Catalyzes the NADPH-dependent formation of L-aspartate-semialdehyde (L-ASA) by the reductive dephosphorylation of L-aspartyl-4-phosphate (PubMed:15752328). Is essential for the growth and pathogenicity of M.tuberculosis, and for the generation of the bacterial cell wall (PubMed:26437401). L-aspartate 4-semialdehyde + NADP(+) + phosphate = 4-phospho-L-aspartate + H(+) + NADPH Amino-acid biosynthesis; L-lysine biosynthesis via DAP pathway; (S)-tetrahydrodipicolinate from L-aspartate: step 2/4. Amino-acid biosynthesis; L-methionine biosynthesis via de novo pathway; L-homoserine from L-aspartate: step 2/3. Amino-acid biosynthesis; L-threonine biosynthesis; L-threonine from L-aspartate: step 2/5. Homodimer. Deletion of this gene inhibits bacterial growth. The mutant cells lose an average of 77.8% of their cell wall materials, exhibit altered morphology, and have a reduced capacity to infect macrophages. Belongs to the aspartate-semialdehyde dehydrogenase family.