Prolamin storage proteins and alloploidy in wild populations of the small grass Brachypodium distachyon (L.) P. Beauv

This paper reports the glutenin diversity of a collection of 23 wild populations of the grass Brachypodium distachyon collected in the Mediterranean and southern areas of the Iberian Peninsula. The plant material studied included the three different cytotypes of this species: 2n = 10, 2n = 20 and 2n = 30. A specific method of extraction was used to isolate the glutenin subunits from the caryopsis. Separation by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) showed them to correspond to wheat low-molecular-weight glutenin subunits (LMW-GS). Twenty-two LMW-GS–like were identified that showed great diversity within and between populations. All the populations investigated were polymorphic for the endosperm proteins studied. The 2n = 30 forms had the largest number of subunits; these were also more diverse than those of the 2n = 10 or 2n = 20 forms. The 2n = 10 forms, the most common in the higher, interior areas of the Iberian Peninsula, showed the smallest subunit variation. In fact, negative correlations were found between subunit diversity and altitude and longitude. In contrast, a positive correlation was detected with the annual average temperature and the indices of thermicity and Mediterraneity. The similarity between the populations was estimated using the Sorensen–Dice coefficient, calculated on the basis of the presence/absence of the 22 LMW-GS proteins. The similarity indices were used to produce a dendrogram using the unweighted pair-group method with arithmetic means (UPGMA). This method produced three main groups corresponding to the three cytotypes. An analysis was made of the possible correlation between eco-geographic and climatic factors and the gene diversity and polymorphism shown in the populations. The diversity correlated positively with the number of chromosomes (2n), annual mean temperature, index of thermicity and index of Mediterraneity. In contrast, diversity correlated negatively with altitude, longitude and index of precipitation during the summer. The number of chromosomes correlated negatively with altitude, longitude and precipitation during summer and positively with all the other climatic indices. These results are coherent with the fact that diploid forms were more common in areas of the interior and at higher altitude, where the climate is more extreme.