The Maize Transposable Element Ds Is Spliced from RNA

Abstract

In some instances, insertion of maize transposable elements into exons does not result in the total loss of enzymatic activity. In other instances, messenger RNAs of wild-type size are encoded by genes known to contain the maize transposable element Dissociation (Ds) in exons. To understand how Ds is processed from RNA, a study was made of transcripts encoded by two alleles of the maize waxy (wx) gene containing Ds insertions in exon sequences. The analysis was carried out in strains where the Ds element could not excise from the wx gene. Despite insertions of 4.3- and 1.5-Ds elements, the predominant transcripts encoded by these two genes were wild type in size. For both alleles, DNA sequencing of complementary DNAs revealed that the Ds elements had been spliced in a similar manner. Splicing was accomplished by the utilization of multiple 5' donor splice sites in the Ds termini and a 3' acceptor site within the wx gene adjacent to the Ds element. The net effect in both cases was the removal of most of the Ds element from the messenger RNA.

The maize transposable Ds1 element is alternatively spliced from exon sequences.

“…In addition to these examples, the null Ds alleles wx-B4 and AdhJ-2FJJ encode non-mutantsize Wx or Adhl transcripts (5,32). Surprisingly, molecular cloning and DNA sequence analysis revealed that these leaky and null alleles contain exon insertions and that all, except Adhi-Fm335, contain insertions in translated exons (5,6,24,27,32).…”

“…Certain Dissociation (Ds)-and defective-suppressor-mutator (dSpm)-containing alleles of the maize alcohol dehydrogenase 1 (AdhilFm335), waxy (wx-m9), and bronze (bz-m13, bz-m13CS9) genes display a stable intermediate or nonmutant phenotype in strains in which these elements cannot transpose, that is, in the absence of the autonomous Activator (Ac) or Spm element (16,19,21,24). In addition to these examples, the null Ds alleles wx-B4 and AdhJ-2FJJ encode non-mutantsize Wx or Adhl transcripts (5,32). Surprisingly, molecular cloning and DNA sequence analysis revealed that these leaky and null alleles contain exon insertions and that all, except Adhi-Fm335, contain insertions in translated exons (5,6,24,27,32).…”

“…Wx encodes a starch granule-bound ADP-glucose glucosyl transferase that is responsible for amylose biosynthesis in the endosperm and pollen (20). The leaky wx-m9 allele and the null wx-B4 allele encode non-mutant-size Wx mRNAs, despite the presence of 4.3-and 1.4-kb Ds elements, respectively, in translated exons (32). For both alleles, the Ds elements can be alternatively spliced from pre-mRNAs if one of three 5' splice sites clustered within 20 bp near the Ds terminus is joined to a 3' splice site within the Wx gene adjacent to the Ds element (32).…”

“…In addition to these examples, the null Ds alleles wx-B4 and AdhJ-2FJJ encode non-mutantsize Wx or Adhl transcripts (5,32). Surprisingly, molecular cloning and DNA sequence analysis revealed that these leaky and null alleles contain exon insertions and that all, except Adhi-Fm335, contain insertions in translated exons (5,6,24,27,32).To understand how genes containing large transposable elements in translated exons can encode functional products, wild-type-size products or both, we have focused on several Ds alleles of the waxy (Wx) gene. Wx encodes a starch granule-bound ADP-glucose glucosyl transferase that is responsible for amylose biosynthesis in the endosperm and pollen (20).…”

Nuclear pre-mRNA processing in plants: distinct modes of 3'-splice-site selection in plants and animals.

“…(ii) In the case of a cauliflower mosaic virus strain which contains a mutation resulting in a partial processing of the cauliflower mosaic virus 35S RNA (in the wild-type strain the 35S RNA does not appear to be spliced), it is one of the most A+U-rich RNA regions that is spliced out (18). (iii) Transposable element sequences located in the coding regions of different maize genes are frequently spliced out, partially restoring a wild-type phenotype (21,44,47,51). In most instances, the A+U content of these sequences is high.…”