TCA MICROSATELLITE REPEATS IN THE 59UTR OF THE Sat5 GENE OF WILD AND CULTIVATED ACCESSIONS OF PISUM AND OF FOUR CLOSELY RELATED GENERA

PsSat5, a cDNA clone from Pisum sativum cv. Alaska, contained a microsatellite consisting of 15 TCA repeats within the 59UTR. This SSR microsatellite was immediately upstream of the presumptive ATG start codon. PCR amplification of genomic DNA from cv. Alaska yielded an identical sequence. This repeat region was analyzed from 10 additional wild and cultivated accessions of Pisum and from four closely related genera (Cicer, Lathyrus, Lens, and Vicia). All of the sequences were generally quite similar, with the exception of the number of TCA repeats (region 3) and a short domain immediately upstream of the repeats (region 2). Pisum humile-northern and Lathyrus each contained four TCA repeats (the fewest number observed). Similar to P. sativum-Alaska and other cultivated peas, Lens contained 15 repeats, the largest number observed. The number of TCA repeats does not appear to correspond to the established phylogeny of these accessions, so the cellular events that generated variable numbers of repeats probably have occurred repeatedly and have involved both expansions and contractions in the number of repeats. The mRNA corresponding to PsSat5 was found in all tissues of P. sativum-Alaska that were examined, but its abundance in leaves and sepals was low. The level of expression was similar in growing and nongrowing stems, roots, and axillary buds. Northern blot analysis of stems and leaves of all 15 accessions showed similar levels of expression. Therefore, there is not a clear correlation between the number of TCA repeats in the 59UTR and the level of Sat5 expression.