Identification of a new class of pistil-specific proteins of Petunia inflata that is structurally similar to, but functionally distinct from, the self-incompatibility factor HT
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Pollen–pistil interactions are thought to involve a wide variety of intercellular recognition events controlled by diverse proteins and other molecules. One of the best characterized interactions is the S-RNase-based gametophytic self-incompatibility (GSI) system found in Solanaceae, Rosaceae and Scrophulariaceae. Although the S specificity of the pistil and the pollen in these families is determined by the S locus-encoded proteins S-RNase and SLF/SFB, respectively, these proteins alone are not sufficient for operation of the GSI reaction. Other factors are also required and are classified into three groups. To date, the only known factor is the pistil-expressed small asparagine-rich protein HT-B in three solanaceous genera Nicotiana, Lycopersicon and Solanum. HT-B is a Group 2 factor that is required for pollen rejection but do not affect S-RNase expression; factors in the other groups have not yet cloned. Here, we identified a new class of HT-like proteins in the style of Petunia inflata and named it HTL. Through alternative splicing, it was found that two isolated homologous HTL cDNAs, HTL-A and HTL-B, derived from a single gene. Like HT-B, HTL showed pistil-specific accumulation as well as significant sequence similarity to HT including conserved cystein residues at the C-terminal region and a signal peptide for extracellular localization. However, unlike HT-B, HTL lacked an asparagine-rich domain. Thus, it represents a new class of HT proteins. To determine whether HTL is involved in GSI function, RNA silencing constructs for HTL-A and HTL-B were introduced into self-incompatible P. inflata. Although several transgenic lines showed no detectable levels of both HTL-A and HTL-B transcripts, they retained normal GSI function and produced large fruits upon compatible pollination. This suggests that since silencing of the HTL gene alone is not sufficient to affect reproductive physiology, the gene is functionally distinct from the GSI factor HT-B.
KeywordsPetunia Pollen–pistil interactions RNA silencing Self-incompatibility
We thank Dr. J.B. Power for P. inflata seeds, Dr. P.M. Waterhouse for pHANNIBAL, Dr. A.P. Gleave for pART27 and Dr. W.J. Stiekema for pBINPLUS. Drs. Y. Ogawa, Y. Hoshino and H. Washida are acknowledged for their technical advice. We also thank Melody Kroll for proof reading this manuscript. This work was supported in part by the Grants-in-Aid for Scientific Research (C, 13660011) and the Grants-in-Aid for Young Scientists (A, 16688001) from the Ministry of Education, Science, Sports and Culture of Japan to H.S.
- de Nettancourt D (2001) Incompatibility and incongruity in wild and cultivated plants. Springer, Berlin Heidelberg New YorkGoogle Scholar
- Doyle JJ, Doyle JL (1990) Isolation of plant DNA from fresh tissue. Focus 12:13–15Google Scholar
- O’Brien M, Kapfer C, Major G, Laurin M, Bertrand C, Kondo K, Kowyama Y, Matton DP (2002) Molecular analysis of the stylar-expressed Solanum chacoense small asparagine-rich protein family related to the HT modifier of gametophytic self-incompatibility in Nicotiana. Plant J 32:985–996CrossRefPubMedGoogle Scholar
- Olmstead RG, Sweere JA, Spangler RE, Bohs L, Palmer JD (1999) Phylogenetic and provisional classification of the Solanaceae based on chloroplast DNA. In: Nee M, Symon DE, Lester PN, Jessop JP (eds) Solanaceae IV. Royal Botanic Gardens, Kew, pp 111–137Google Scholar
- Qiao H, Wang H, Zhao L, Zhou J, Huang J, Zhang Y, Xue Y (2004) The F-box protein AhSLF-S2 physically interacts with S-RNases that may be inhibited by the ubiquitin/26S proteasome pathway of protein degradation during compatible pollination in Antirrhinum. Plant Cell 16:571–581CrossRefPubMedGoogle Scholar
- Sassa H, Hirano H, Ikehashi H (1992) Self-incompatibility-related RNases in styles of Japanese pear (Pyrus serotina Rehd.). Plant Cell Physiol 33:811–814Google Scholar