Hop1, encoding a homeodomain-containing   transcription factor, is located near Prx3 on linkage group VI

Homeodomain-containing transcription factors have been shown to determine cell fate or convey positional information during the development of many multicellular organisms (1, 4). Many plant homeodomain proteins are also referred to as KNOX genes (for knotted-like homeobox) and come in at least two types: class 1, which are expressed primarily in meristematic tissue and class 2, which display a more diverse expression (3, 4). It is possible that several pea mutants, including af, uni, and/or sil, might, in some way, be related to expression of KNOX genes, and the laboratory of the second author has been pursuing this possibility. A 1778 bp pea cDNA clone was isolated by Giles et al. (2) that contained two possible open reading frames (ORFs): a 93 bp upstream ORF (uORF) and a 1113 bp KNOX-like ORF. In order to assess whether this clone could correspond to one of the morphological mutants known in pea, we mapped its position on the consensus map of pea (5). Here we present the details of the mapping experiments.

Oligonucleotide primers were designed from the Hop1 cDNA sequence as follows: HOP1-F = 5’-CTT ACA CTA ACC CTT GTT CC and HOP1-R = 5’-CAT CAC CAC CCA TTC TCA CT. At 62°C annealing temperature, these primers amplified a single product when pea DNA was used as a template. DNA from the two parents, JI1794 and Slow, of our mapping population were used as template for PCR amplification reactions. Comparison of restriction fragment patterns generated from the JI1794 product with that from the Slow product revealed differences for HaeIII and HinfI. Restriction fragment patterns were then obtained for the PCR products generated from the DNA extracted from each of 44 recombinant inbred lines (RILs) from our JI1794 x Slow mapping population. The results gave 22 patterns corresponding to the JI1794 parent and 22 patterns identical to the Slow parent. The segregation of the patterns assorted independently of all 800-plus markers on the map except those clustered around Gsp and Prx3 on linkage group VI. The Hop1 data gave four recombinants with Prx3, four with Gsp, three with a RAPD produced by the 10-mer B446 (5’-GCCAGCGTTC), two with a RAPD produced by the 10-mer OM12 (5’-GGGACGTTGG), and none with the RAPD produced by the 10mer P123 (5’-GGGATTCGAC). The approximate map location is therefore:

This position does not correspond to that of any leaf or other mutation that might be attributable to a defect in a KNOX gene.