The genomic relationship between Glycine max (L.) Merr. and G. soja Sieb. and Zucc. as revealed by pachytene chromosome analysis

Abstract

This study was conducted with the objective of determining the genomic relationship between cultivated soybean (Glycine max) and wild soybean (G. soja) of the subgenus Soja, genus Glycine. Observations on cross-ability rate, hybrid viability, meiotic chromosome pairing, and pollen fertility in F 1 hybrids of G. max × G. soja and reciprocals elucidated that both species hybridized readily and set mature putative hybrid pods, generated vigorous F1 plants, had a majority of sporocytes that showed 18II + 1IV chromosome association at diakinesis and metaphase I, and had a pollen fertility that ranged from 49.2% to 53.3%. A quadrivalent was often associated with the nucleolus, suggesting that one of the chromosomes involved in the interchange is a satellited chromosome. Thus, G. max and G. soja genetic stocks used in this study have been differentiated by a reciprocal translocation. Pachytene analysis of F1 hybrids helped construct chromosome maps based on chromosome length and euchromatin and heterochromatin distribution. Chromosomes were numbered in descending order of 1-20. Pachytene chromosomes in soybean showed heterochromatin distribution on either side of the centromeres. Pachytene analysis revealed small structural differences for chromosomes 6 and 11 which were not detected at diakinesis and metaphase I. This study suggests that G. max and G. soja carry similar genomes and validates the previously assigned genome symbol GG.

A Fluorescence in Situ Hybridization System for Karyotyping Soybean

“…2019), a cultivar originating from Jilin province, in northeast China and maintained in the USDA Soybean Germplasm Collection (http://www.ars-grin.gov/). Although the cytogenetics of G. soja (2n ¼ 40) were previously studied (Ahmad et al 1984;Singh and Hymowitz 1988), most wild soybean accessions have not been mapped by molecular or classical genetic markers. Therefore, chromosome assignments based on positioned G. max W82 BACs should be viewed as tentative.…”

“…This was resolved by assigning chromosome numbers on the basis of molecular and genetic recombination distances (centimorgans), which do not necessarily correspond to physical distances (micrometers) or cytological size. This approach may have resulted in the numbering of soybean chromosomes in direct contradiction to the original cytologically determined chromosome designations (Singh and Hymowitz 1988).…”

“…The first cytological description of domesticated soybean, Glycine max [L.] Merr. (G. max) (2n ¼ 40), was developed using pachytene chromosomes, which were numbered from 1 to 20 on the basis of total chromosome length, arm length ratios, and relative proportions of euchromatin and heterochromatin (Singh and Hymowitz 1988). Primary trisomic lines (2x 1 1 ¼ 41; Xu et al 2000) were used to associate 11 of the 20 MLGs with cytologically numbered chromosomes (Cregan et al 2001;Zou et al 2003).…”

“…The cytological study of soybean metaphase chromosomes has been challenging for several reasons: first, the chromosomes are small, on the order of $1-2 mm in length (Sen and Vidyabhusan 1960;Clarindo et al 2007); second, the 20 pairs of soybean chromosomes (Veatch 1934) make FISHmapping challenging; and third, these 20 chromosome pairs show little morphological diversity. With the exception of a single acrocentric pair, soybean chromosomes are all metacentric or submetacentric (supporting information, Figure S1; Ahmad et al 1984;Singh and Hymowitz 1988;Clarindo et al 2007), making them difficult to distinguish in routine mitotic preparations. Moreover, the low mitotic index characteristic of soybean root meristems (Ahmad et al 1983) renders chromosome preparation for karyotyping quite inefficient.…”

National Science Foundation-Sponsored Workshop Report. Draft Plan for Soybean Genomics

“…This makes it about seven and one-half times larger than the genome of Arabidopsis but less than one-half the size of the maize genome (Arumuganathan and Earle, 1991). A complete karyotype of soybean has been reported (Singh and Hymowitz, 1988) based upon pachytene analysis (http://www.cropsci.uiuc.edu/faculty/ hymowitz/genlab/karyo.html). More than 35% of the genome is made up of heterochromatin, with the short arm of 6 of the 20 bivalents being completely heterochromatic (Singh and Hymowitz, 1988).…”