MOLECULAR-CLONING AND CHARACTERIZATION OF 6 CDNAS EXPRESSED DURING GLUCOSE STARVATION IN EXCISED MAIZE (ZEA-MAYS L) ROOT-TIPS

In order to isolate glucose-starvation-related cDNAs in maize (Zea may s L.) root tips, a cDNA library was constructed with poly(A)(+) mRNA f rom 24 h starved root tips. After differential screening of the librar y, we isolated six different cDNAs (named pZSS2 and pZSS7) which were expressed during glucose starvation. Time course analysis revealed tha t maximum expression of five of these genes occurs 30 h after the onse t of the starvation treatment. On the contrary, the expression of mRNA s corresponding to pZSS4 was maximal at an early stage of starvation a nd then dramatically decreased. The expression of this gene did not se em to be specific for glucose starvation. The pattern of induction of the genes corresponding to pZSS2, pZSS3, pZSS5, pZSS6 and pZSS7 reveal ed that non-metabolizable sugars such as L-glucose and mannitol induce mRNA transcription similarly to glucose starvation. When D-glucose or any other metabolizable sugar was supplied, the level of transcripts was reduced. Nucleotide sequence analyses of the six cDNAs allowed ide ntification of five of them by comparison with sequence data bases. Th e protein encoded by clone pZSS2 is analogous to a wound-induced prote in from barley. Clones pZSS4 to pZSS7 encode, respectively, a transmem brane protein, a cysteine protease, a metallothionein-like protein and a chymotrypsin/subtilisin-like protease inhibitor. Clone pZSS3 shares no significant homology with any known sequence.