Molecular characterization of the ribulose bisphosphate carboxylase/oxygenase multigene family in hexaploid wheat

Abstract

Ribulose bisphosphate carboxylase/oxygenase (rubisco, EC 4.1.1.39) catalyzes the first step in the Calvin pentose phosphate cycle. It is composed of eight large subunits and eight small subunits. The large subunits are encoded by chloroplast genes (rbcL) and the small subunits are encoded by a nuclear multigene family (rbcS). In this research, the number of rbcS genes in hexaploid wheat Triticum aestivum var. Chinese Spring was estimated, their chromosome-arm locations were determined, two major gene subfamilies were characterized and evolutionary relationships among the family members were described. The gene locations were determined by Southern blot hybridizations of DNA extracted from aneuploid derivatives of wheat variety Chinese Spring. Several Southern blot hybridization experiments were performed in which a 530 bp piece of DNA from exon II of a rbcS gene from wheat (inserted into the pTaySs 3.2) was used as a probe to determine the chromosome locations of the rbcS genes. The results indicate that rbcS genes are located in the long arms of the homoeologous group 5 chromosomes (5AL, 5BL and 5DL) and in the short arms of the homoeologous group 2 chromosomes (2AS, 2BS and 2DS). The rbcS gene family members in hexaploid wheat were divided into more divergent gene subfamilies by using two different 3' end specific probes, designated 3' end probe I and 3' end probe II, in Southern blot hybridization analysis of hexaploid wheat aneuploids. It was found that the rbcS multigene family consists of at least two divergent gene subfamilies. One of them is a small subfamily, rbcS-1, consisting of about three copies per polyhaploid genome. The members of this subfamily are located in 5AL, 5BL and 5DL. The second subfamily, rbcS-2, is large, consisting of about nine copies per polyhaploid genome. The members of this subfamily are distributed between the chromosomes of homoeologous groups 2 and 5. Because of the fact that these two subfamilies do not include every rbcS gene, it is suggested that there exists at least one other subfamily that has not yet been identified...