Sequence variability and gene structure at the self-incompatibility locus of Solanum tuberosum

Abstract

Allelic complexity is a key feature of self-incompatibility (S) loci in gametophytic plants. We describe in this report the allelic diversity and gene structure of the S locus in Solanum tuberosum revealed by the isolation and characterization of genomic and cDNA clones encoding S-associated major pistil proteins from three alleles (S1, Sr1, S2). Genomic clones encoding the S1 and S2 proteins provide evidence for a simple gene structure: Two exons are separated by a small intron of 113 (S1) and 117 bp (S2). Protein sequences deduced from cDNA clones encoding S1 and Sr1 proteins show 95% homology, 15 of the 25 residues that differ between these S1 and Sr1 alleles are clustered in a short hypervariable protein segment (amino acid positions 44-68), which corresponds in the genomic clones to DNA sequences flanking the single intron. In contrast, these alleles are only 66% homologous to the S2 allele, with the residues that differ between the alleles being scattered throughout the sequence. DNA crosshybridization experiments identify a minimum of three classes of potato S alleles: one class contains the alleles S1, Sr1 and S3, the second class S2 and an allele of the cultivar Roxy, and the third class contains at present only S4. It is proposed that these classes reflect the origin of the S alleles from a few ancestral S sequence types.

The F-Box Protein AhSLF-S2 Controls the Pollen Function of S-RNase–Based Self-Incompatibility

“…Nevertheless, in some cases, S-RNase alleles share very high similarity, for example, S 1 -and S r1 -RNase in Solanum tuberosum (Kaufmann et al, 1991) and S 11 -and S 13 -RNases in S. chacoense (Despres et al, 1994;Saba-el-Leil et al, 1994) all show >95% homology and yet they are phenotypically distinct. Despite the low degree of polymorphism of four AhSLF alleles (;95% identity) (Zhou et al, 2003) and three PiSLF alleles (;90% identity) (Sijacic et al, 2004) compared with PdSFB and PmSLF alleles (;68 to 80% similarity) (Entani et al, 2003;Ushijima et al, 2003;Yamane et al, 2003), the alteration of the pollen function by AhSLF-S 2 clearly shows that this Antirrhinum F-box gene is capable of determining male specificity.…”

Origin of allelic diversity in antirrhinum S locus RNases.

“…Black dots are gaps introduced to maximize the alignment. S RNases include sequences from Antirrhinum (52, S4, and S5), apple (S2mdo and S3mdo) (Broothaerts et ai., 1995), Lycopersicon peruvianum (Lpslgs6 and Lps5b) Rivers et al, 1993), Solanum tuberosum (Sts2) (Kaufmann et al, 1991), Petunia hybrida (Phs3) (Clark et al, 1990), f ? inflata (Pis3) (Ai et al, 1990), Nicotiana alata (S2nic) (Anderson et al, 1986), and S. cbacoense (Scs3) (Xu et al, 1990).…”

Gametophytic Self-Incompatibility Systems.

“…of the mature protein as well as several other conserved sequences, as depicted in Figure 4. This information allowed the cloning of cDNAs corresponding to further S alleles of N. alata and S alleles from Petunia inflata (Ai et al, 1990), Solatium chacoense (Xu et al, 1990), P hybrida (petunia; Clark et al, 1990), Solanum tubemsum (potato; Kaufmann et al, 1991), and Lycopersiconperuvianum (Tsai et al, 1992). Alignment of all these sequences (Tsai et al, 1992) shows that, overall, ~16°/o of the amino acids are identical, including eight cysteine residues.…”

“…The finding that the S-glycoproteins have RNase activity has led to their being referred to as S-RNases. Subsequently, S-glycoproteins from other solanaceous species have been shown to have RNase activity (Broothaerts et al, 1991;Kaufmann et al, 1991;Singh et al, 1991;Ai et al, 1992). In addition, RNases have been detected in the styles of Japanese pear (a member of the family Rosaceae), and it is possible that these are also S-related glycoproteins (Sassa et al, 1992).…”