1476.6.2 Ph -Like Genes in Wheat Related Species
6.6.2.1 Ae. speltoides
Many studies have rep orted the ability of certain genotypes of the outcrossing spe-
cies Ae. speltoides to induce wheat–alien pairing even in the presence of Ph1 (e.g.,
Maestra and Naranjo 1998 ; see Table 6.2 ). Since promoter genes of Ae. speltoides
behave as epistatic to Ph genes of wheat, these genes have been generically desig-
nated as Ph I^ (inhibitors of Ph ) (Chen et al. 1994 ).
The fi rst evidence on the existence of Ph I^ genes in Ae. speltoides was communi-
cated soon after the identifi cation of a meiotic control activity on wheat chromo-
some arm 5BL (Riley et al. 1961 ). Crossing with Ae. speltoides was indeed the
critical intermediate step of the backcrossing program that resulted in the obtention
of ‘Compair’, the fi rst wheat line incorporating a useful alien trait by ge netic induc-
tion of homoeologous recombination (Riley et al. 1968 ). Allelic variation for Ae.
speltoides genes interacting with the wheat dip loidizing meiotic control system was
also reported (Dvořák 1972 ).
Promoter genes were successfully transferred from a high-pairing accession of
Ae. speltoides to hexaploid wheat Chinese Spring by Chen et al. ( 1994 ). These Ph I^
wheat stocks have demonstrated to be effective in inactivating the Ph system in
varied wheat–alien hybrid combinations (Aghaee-Sarbarzeh et al. 2000 ).
Chen and Dvořák ( 1984 ) proposed that the genetic system in Ae. speltoides is
controlled by two major genes, with different effectiveness and additive effects, in
addition to some minor genes. This w as supported by the segregation of low, inter-
mediate, and high chromosome pairing phenotypes in the progenies of Ph I^ wheat
lines differing in their wheat– alien homoeologous pairing promoting effect (Chen
et al. 1994 ). The presence of a structurally modifi ed chromosome 4D in Ph I^ wheat
lines as well as its altered pairing behavior led also to suggest that a high-pairing
gene(s) was introgressed as a 4S segment transferred on 4D (Chen et al. 1994 ).
By using a QTL mapping approach, Dvǒrák and coworkers have detected two
Ae. speltoides genes with major suppressing effect on Ph1 activity (Dvořák et al.
2006 ). These genes, designated as Su1 - Ph1 and Su2 - Ph1 , locate on the long arm of
chromosomes 3S and 7S, respectively. Su1 - Ph1 , with a greater promoting effect on
homoeologous chromosome pairing, is epistatic to Su2 - Ph1. These authors mapped
also a QTL with a minor effect on the short arm of chromosome 5S, a fi nding sup-
ported by the observations of multivalents in wheat lines where 5B is substituted by
5S (Friebe et al. 2011 ). Based upon the failure to map any of the major Ph1 suppres-
sors on chromosome 4S, Dvǒrák and coworker s concluded that neither Su1 - Ph1 nor
Su2 - Ph1 were the genes operating in Ph I^ lines. This is consistent with the absence
of Ae. speltoides species-specifi c amplifi cation products for SSR markers located
on the long arm of group-3 and -7 chromosomes in three CS- Ph I^ lines r eported by
Li et al. ( 2011 ).
The molecular tagging of Ph I^ is being approached. Meanwhile, the Ph I^ lines have
been successfully employed for the incorporation into wheat chromosomes of alien
6 The Mode and Regulation of Chromosome Pairing...