Has a housekeeping role in isoleucine biosynthesis (Probable). L-threonine = 2-oxobutanoate + NH4(+) Strongly inhibited by 1 mM isoleucine. Active at alkaline pH. Optimum temperature is 16 degrees Celsius. Not active at temperatures above 55 degrees Celsius. Complete loss of activity by incubation at 55 degrees Celsius for 1 min. Amino-acid biosynthesis; L-isoleucine biosynthesis; 2-oxobutanoate from L-threonine: step 1/1. Expressed constitutively in all tissues examined including root, stem, petiole, leaf, immature flower bud, unopened flower and opened flower with the highest expression in opened flower and lowest in leaf. Constitutively expressed. Not induced in response to methyl jasmonate (MeJA) or mechanical wounding. Belongs to the serine/threonine dehydratase family.