members of group III (Tichtinsky et al., 1998), LpSK6 has an extended N-terminal region, which
contains a potential mitochondrial localization signal with a putative cleavage site (Figure 3).
The Lycopersicon CMS phenotype results from an incompatibility between the cytoplasm of
L. peruvianum and the nuclear genome of L. pennellii and occurs after the tetrad stage (Petrova et
al., 1998; 1999; Vulkova-Achkova, 1980). CMS in general involves the lack of pollen development
due to inadequate mitochondrial function in male reproductive tissue (Hanson, 1991; Kempken and
Pring, 1997). The identification of a GSK gene in the Lycopersicon CMS system, the expression of
its homologues in male reproductive tissues and the conserved mitochondrial localization signal
present in all homologues, indicate the possible involvement of LpSK6 in generating the CMS
and/or fertility restored phenotype.
Acknowledgements
This work was supported in part by seed grant no. 2001-01500 for the U.S. Department of
Agriculture (USDA).
Figure Legends
Figure 1. Differential display gel with amplified anther mRNAs with FHT11G and HAP-1 primers
(GenHunter Co.). Lanes 1 - 5 contain PCR products from L. pennellii, L. peruvianum, L. esculentum,
and CMS-pennellii. Lanes 6 - 8 contain PCR products from 3 hybrid (H) plants F3[CMS – pennellii x
F1(L. esculentum x L. pennellii)] with varying percentage of pollen stainability. The products were
separated on a 6% polyacrylamide denaturing gel and detected by fluorescence. The arrow
indicates the band excised from the H1 lane.
Figure 2. Quantitative RT-PCR of LpSK6 in the plants of the Lycopersicon CMS system: L.
pennellii, L. peruvianum, CMS-pennellii, L. esculentum, and hybrid (H) plants 1, 2, 6 and 8. Lanes
contained RT reactions with reverse transcriptase (+) or control samples without enzyme (-). Top
image shows amplification using LpSK6 primers; bottom image shows amplification of the GADPH
as an internal control.
Figure 3. LpSK6 nucleotide (Genebank accession number AY575716) and amino acid sequences.
The box indicates the putative cleavage site for the mitochondrial localization signal. The two arrows
show the location of the LpSK6 primers used in the quantitative PCR reactions shown in Figure 2.
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