THE CHARACTERIZATION OF TAPETUM-SPECIFIC CDNAS ISOLATED FROM A LILIUM-HENRYI L MEIOCYTE SUBTRACTIVE CDNA LIBRARY

Differential screening of a meiocyte subtractive cDNA library from Lil ium henryi L. has identified a group of 16 anther-specific partial cDN As. Three of these sequences, LHM2, LHM6 and LHM7 have been further ch aracterised. Hybridisation in situ with antisense riboprobes of LHM2, LHM6, and LHM7 gives a strong, clear signal which, contrary to expecta tions, is localised to the tapetal layer surrounding the meiocytes and not the meiocytes themselves. Developmental slot blots demonstrate th at mRNAs corresponding to the three LHM cDNAs are transcribed from pro phase of meiosis I to the uninucleate microspore stage, while Northern analysis reveals these tapetally expressed cDNAs to correspond with t ranscripts of some 500 bp. Although LHM2 is less abundant than LHM6 an d LHM7, the pattern of developmental expression, and the size range of the transcripts suggests that all three cDNAs may be related. The ded uced polypeptide products of LHM6 and LHM7 share 71% identity over a c onserved region of 38 residues. Inverse polymerse chain reaction was u sed to obtain the full sequence for LHM7. Its deduced protein sequence has a signal peptide indicating it may be secreted; the cleaved prote in has a molecular weight of 8.9 kDa. Furthermore, the LHM7 protein ha s significant levels of homology with tapetally expressed proteins fro m Arabidopsis thaliana, Antirrhinum majus and Lycopersicon esculentum. All contain a highly conserved pattern of cysteine residues present i n seed and non-specific lipid transfer proteins. The function of this gene product is discussed in the perspective of current models of anth er development.