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Molecular analysis of two phytohemagglutinin genes and their expression in Phaseolus vulgaris cv. Pinto, a lectin‐deficient cultivar of the bean
Author(s) -
Voelker Toni A.,
Staswick Paul,
Chrispeels Maarten J.
Publication year - 1986
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1986.tb04613.x
Subject(s) - phaseolus , biology , humanities , library science , art , botany , computer science
Phytohemagglutinin (PHA), the seed lectin of the common bean, Phaseolus vulgaris , is encoded by two highly homologous, tandemly linked genes, dlec 1 and dlec 2, which are coordinately expressed at high levels in developing cotyledons. Their respective transcripts translate into closely related polypeptides, PHA‐E and PHA‐L, constituents of the tetrameric lectin which accumulates at high levels in developing seeds. In the bean cultivar Pinto UI111, PHA‐E is not detectable, and PHA‐L accumulates at very reduced levels. To investigate the cause of the Pinto phenotype, we cloned and sequenced the two PHA genes of Pinto, called Pdlec 1 and Pdlec 2, and determined the abundance of their respective mRNAs in developing cotyledons. Both genes are more than 90% homologous to the normal PHA genes found in other cultivars. Pdlec 1 carries a 1‐bp frameshift mutation close to the 5′ end of its coding sequence. Only very truncated polypeptides could be made from its mRNA. The gene Pdlec 2 encodes a polypeptide, which resembles PHA‐L and its predicted amino acid sequence agrees with the available Pinto PHA amino acid sequence data. Analysis of the mRNA of developing cotyledons revealed that the Pdlec 1 message is reduced 600‐fold, and Pdlec 2 mRNA is reduced 20‐fold with respect to mRNA levels in normal cultivars. A comparison of the sequences which are upstream from the coding sequence shows that Pdlec 2 has a 100‐bp deletion compared to the other genes ( dlec 1, dlec 2 and Pdlec 1). This deletion which contains a large tandem repeat may be responsible for the low level of expression of Pdlec 2. The very low expression of Pdlec 1 is as yet unexplained.