A scs^ae gene on chromosome 1D alters the expression of a gametocidal (scs^spt) gene in a T2BL.2S chromosome

S. S. Maan and S. Kianian

Department of Plant Sciences, North Dakota State University, Fargo,ND

Summary

A species cytoplasm specific gene (scs^ae ) on the long-arm of chromosome 1D (1DL) from common wheat (Triticum aestivum L.) produced compatibility of the nuclear genome of durum wheat (T .turgidum L.) with the cytoplasm of D- or M-genome Aegilops species, including an altered cytoplasm of Ae. longissima (lo). Similarly, a 29chromosome durum line with Ae. uniaristata (un) cytoplasm and a un-telocentric homoeologous to group 4 chromosomes, a (lo) durum line with scs^ti in the long-arm of chromosome 1A from T. timopheevi, and a (Ae. ventricosa) durum [(vent) line] with scs^spt in T2BL.2S translocation chromosome having 2S from Ae. speltoides were compatible but male-sterile. Our objective was to determine the transmission of female gametes with scs^ae versus those with scs^ti , scs^un , or scs^spt . We crossed (lo) scs^ti , (un) scs^un , and (vent) scs^spt durum lines to 1D(1A) and 1D(1B) disomic-substitution lines of Langdon durum (LDN DS) and crossed hybrid progeny to the corresponding paternal LDN DS lines as recurrent male parents. The resulting alloM?plasmic LDN DS lines were male sterile and when crossed to paternal LDN DS lines; (lo) and (un) DS lines had complete seed-set and 14 closed chromosome pairs, while (vent) DS lines had partial seed-set, 13 closed chromosome pairs and 1 open pair at the meiotic metaphase I in the pollen mother cells. The results showed that scs^ae replaced scs^ti or scs^un in the (lo) and (un) DS lines, that 2S did not pair with 2BS, and that scs^spt was expressed as a gametocidal (Gc) gene but did not produce chromosomal structural abnormalities in the (vent) 1D(1A) and 1D(1B) DS lines having scs^ae in chromosome 1D.

Key words: interactions among the scs^ae and scs^ti , scs^un , or scs^spt genes, interspecific nucleo-cytoplasmiccompatibility.

Introduction

According to the species cytoplasm specific (scs) gene hypothesis (Maan 1995), the native scs genes produce intraspecific nucleo-cytoplasmic compatibility and male fertility but are expressed as male sterility when the nuclear genome of one species is substituted in the cytoplasm of another by the backcross method of Kihara (1951). The resulting male-sterile lines are maintained by crossing to normal counterparts. Similarly, the parental scs genes are essential components of interspecific sterility when in the hemizygous condition in the species hybrids but add to the fertility when in the homozygous condition in the amphidiploid progeny.

The nuclear genome of common wheat (Triticum aestivum L.; 2n=6x=42, 21", AABBDD) is compatible, but the nuclear genome of durum wheat (T. turgidum L.; 2n=4x=28, AABB) is partially or completely incM?ompatible with the cytoplasm of D- and M-genome Aegilops species (Maan 1975; 1978), including an experimentally altered cytoplasm of Ae. longissima (2n=14, 7", SS) (Maan 1996). A species cytoplasm specific gene (scs^ae ) on the long-arm of chromosome 1D (1DL) from common wheat improved compatibility between durum wheat and the alien cytoplasms, Ae. longissima, Ae. uniaristata (un ) (2n=14, 7", M^uM^u), and Ae. ventricosa (vent ) (2n=28, 14", DDMM) (Maan and Endo 1981, 1991; Tsuji and Maan 1981). The resulting 29-chromosome durum lines with 1D were male sterile and when crossed to normal durum produced plump and viable seeds having 29chromosome embryos with 1DL, while seeds having 28-chromosome embryos (without 1DL) were shrivelled and inviable or they produced male-sterile plants of greatly reduced vigor (Maan 1975, 1978, 1992a, b, c, 1994).

Nucleo-cytoplasmic interactions involving alien cytoplasms and nuclear genomes of durum wheat and common wheat alter the expression of wheat nuclear genes and produce a variety of phenotypes, including reduced male and/or female fertility, delayed maturity, reduced plant vigor, and floral abnormalities in the alloplasmic wheat lines (Kihara 1951; Maan 1975, 1978). The species cytoplasm specific (scs) genes producing nucleo-cytoplasmic compatibility may mutate cytoplasm (Maan 1996), or modify the expression of other scs genes in the euplasmic (Kihara 1951, 1982) or alloplasmic wheat lines. For example, R5, an elite R-line of common wheat produced fertile F₁ and F₂-derived advanced generation progeny that included fertile lines with greatly reduced plant vigor and fertile lines with normal vigor plants (Gomaa 1973; Gomaa and Lucken 1973; Maan unpubl), indicating that the R5 had mutant scsscs and ViVi (vitality) in addition to the male fertility restorer (Rf) genes. Similarly, a gene for black color glumes in a Ae. caudata chromosome homeologous group 1 produced fertility in (Ae. caudata) common wheat line and frequently mutorated and produced non-black glumes when hemizygous in the cytoplasmic background of normal common wheat (Kihara 1951, 1982).

Similarly, Vi, a gene mutant at the latent Rf₂ locus in the short arm of chromosome 1B of durum wheat, chromosome 1B of Chinese Spring wheat (Maan unpubl) and T. spelta var. duhamelianum (Tahir and Tsunewaki 1969) had a positive zenia effect on seed plumpness and produced a male fertile (lo) 29-chromosome durum line having scs^ae in 1DL and a (un ) 29-chromosome durum line having scs^un on un-telocentric homoeologous to group 4 chromosomes (Maan unpubl), while seeds having 28-chromosome embryos (without scs^ae or scs^un ) produced partially fertile plants of greatly reduced vigor (Maan 1992a, b, c, 1994). Also, Vi produced fertility in a (lo) durum line (2n=28, 14") having a scs^ti gene from T. timopheevi Zhuk. (2n=28, 14", AAGG) located in the long arm of chromosome 1A, while seeds with Vi but without scs^ti produced partially fertile plants of greatly reduced vigor (Anderson and Maan 1995).

Tsujimoto and Tsunewaki (1988) reported that common wheat having short arm of chromosome 2S from Ae. speltoides (homoeologous to 2BS of common wheat) had a gametocidal (Gc) gene. Similarly, Maan and Kianian (2001) reported that a scs^spt gene on a T2BL.2S translocation chromosome consisting of the short arm of chromosome 2S from Ae. speltoides and the long arm of chromosome 2B of durum wheat produced compatibility with (vent ) cytoplasm and the resulting (vent ) scs^spt durum line was male sterile, scs^spt was expressed as a gametocidal (Gc) gene, and produced chromosomal stroructural abnormalities in the (vent ) durum line.

Our objective was to determine the relative transmission of scs^ae versus scs^ti , scs^un , and scs^spt genes through the female gametes of (lo) , (un ) and (vent ) durum lines, respectively.

*Corresponding author, E-mail: s.kianian@ndsu.nodak.edu