No abstract

The developing cereal grain accumulates large quantities of proteins which are unique to the endosperm tissue. The DNA sequences which determine their endosperm‐specific expression have not yet been identified. In the absence of a suitable transformation‐regeneration system for cereals, we have investigated whether chimaeric genes consisting of low mol. wt (LMW) and high mol. wt (HMW) glutenin gene upstream sequences coupled to the coding region of the bacterial chloramphenicol acetyl transferase (CAT) gene could be specifically expressed in transgenic tobacco. The fusions, made in a Ti‐derived binary vector, were introduced into tobacco via Agrobacterium tumefaciens‐mediated transformation and their activity assayed. Both the LMW and HMW glutenin chimaeric genes exhibited endosperm‐specific CAT activity in the transformed plants. In addition, a deletion series of the LMW glutenin sequence indicated that sequences present between 326 bp and 160 bp upstream of the transcription start point are necessary to confer endosperm‐specific CAT activity.

The effects of overexpression of two Brassica CBF/DREB1-like transcription factors (BNCBF5 and 17) in Brassica napus cv. Westar were studied. In addition to developing constitutive freezing tolerance and constitutively accumulating COR gene mRNAs, BNCBF5- and 17-overexpressing plants also accumulate moderate transcript levels of genes involved in photosynthesis and chloroplast development as identified by microarray and Northern analyses. These include GLK1- and GLK2-like transcription factors involved in chloroplast photosynthetic development, chloroplast stroma cyclophilin ROC4 (AtCYP20-3), beta-amylase and triose-P/Pi translocator. In parallel with these changes, increases in photosynthetic efficiency and capacity, pigment pool sizes, increased capacities of the Calvin cycle enzymes, and enzymes of starch and sucrose biosynthesis, as well as glycolysis and oxaloacetate/malate exchange are seen, suggesting that BNCBF overexpression has partially mimicked cold-induced photosynthetic acclimation constitutively. Taken together, these results suggest that BNCBF/DREB1 overexpression in Brassica not only resulted in increased constitutive freezing tolerance but also partially regulated chloroplast development to increase photochemical efficiency and photosynthetic capacity.

A gene encoding the high-molecular-weight (HMW) subunit of glutenin 1Ax1 was isolated from bread wheat cv Hope. Comparison of the deduced amino acid sequence with that previously reported for an allelic subunit, 1Ax2(*), showed only minor differences, which were consistent with both subunits being associated with good bread-making quality. Quantitative analyses of total protein extracts from 22 cultivars of bread wheat showed that the presence of either subunit 1Ax1 or 1Ax2(*), when compared with a null allele, resulted in an increase in the proportion of HMW subunit protein from ca. 8 to 10% of the total. It is suggested that this quantitative increase in HMW subunit protein may account for the association of 1Ax subunits with good quality.