Differential expression of four genes encoding 1-aminocyclopropane-1-carboxylate synthase in Lupinus albus during germination, and in response to indole-3-acetic acid and wounding

1-Aminocyclopropane-1-carboxylate (ACC) synthase (ACS; EC 4.4.1.14) is the key regulatory enzyme of the ethylene biosynthetic pathway and is encoded b y a multigene family in Arabidopsis thaliana tomato, mung bean and other pl ants. Southern blot analysis revealed the existence of at least five ACS ge nes in white lupin (Lupinus albus L.) genome. Four complete and one partial sequences representing different ACS genes were cloned fi om the lupin gen omic library. The levels of expression of two of the genes, LA-ACS1 and LA- ACS3, were found to increase after hypocotyl wounding. Apparently, these tw o genes were up-regulated by exogenous IAA treatment of seedlings. The LA-A CS3 mRNA levels were also elevated in the apical part of hypocotyl, which i s reported to contain a high endogenous auxin concentration. This gene may be involved in the auxin- and ethylene-controlled apical hook formation. Th e expression of the LA-ACS4 gene was found to be almost undetectable. This gene may represent a "silent" twin of LA-ACS5 as these two genes share a co nsiderable level of homology in coding and non-coding regions. The LA-ACS5 mRNA is strongly up-regulated in the embryonic axis of germinating seeds at the time of radicle emergence, and was also found in roots and hypocotyls of lupin seedlings.