The origin of exon 3 skipping of paternal GLOBOSA pre-mRNA in some Nicotiana tabacum lines correlates with a point mutation of the very last nucleotide of the exon

Pre-mRNA alternative splicing as a modulator for heat stress response in plants

The molecular responses of plants to the important abiotic stress, heat stress (HS), have been extensively studied at the transcriptional level. Alternative splicing (AS) is a post-transcriptional regulatory process in which an intron-containing gene can generate more than one mRNA variant. The impact of HS on the pre-mRNA splicing process has been reported in various eukaryotes but seldom discussed in-depth, especially in plants. Here, we review AS regulation in response to HS in different plant species. We discuss potential molecular mechanisms controlling heat-inducible AS regulation in plants and hypothesize that AS regulation participates in heat-priming establishment and HS memory maintenance. We propose that the pre-mRNA splicing variation is an important regulator of plant HS responses (HSRs).

T-homoeolog specific plasma membrane protein 3 [Nt(t)PMP3-2] in polyploid Nicotiana tabacum shows conserved alternative splicing, derived from extant Nicotiana tomentosiformis parent

Abiotic stress induced plasma membrane protein 3 (PMP3) genes occur as multigene families in plants, coding for hydrophobic proteins. Group I PMP3s code for shorter ORFs while Group II PMP3s code for proteins with C-terminal extensions. Allotetraploid Nicotiana tabacum (SSTT; 2n = 48) derives its parentage from extant ancestors related to Nicotiana sylvestris (SS) and Nicotiana tomentosiformis (TT). Polyploidization triggers complex genetic and epigenetic changes, often leading to homoeolog-specific retention or loss of function, sub-functionalization or neo-functionalization. Genomic sequences of Nt(t)PMP3-1/Nt(t)PMP3-2 cloned from N. tabacum show near identity with N. tomentosiformis NtoPMP3-1/NtoPMP3-2 genomic sequences respectively (distinct from N. sylvestris NsPMP3-1/NsPMP3-2 genomic regions). RT-PCR with exon 1,2 primer pairs amplified only single fragments for Nt(t)PMP3-1 and Nt(t)PMP3-2. In contrast, for Nt(t)PMP3-2, three variants were detected using exon 2,3 primers by RT-PCR. Cloning revealed (i) a transcript coding for a Group I PMP3 [Nt(t)PMP3-2CS], (ii) a transcript with complete retention of the second intron [Nt(t)PMP3-2IR] and (iii) a transcript with an alternative (exon 2) 5' splice site [Nt(t)PMP3-2AS], coding for a longer protein, similar to ORFs of Group II PMP3 genes. All three Nt(t)PMP3-2 variants have conserved counterparts in the N. tomentosiformis transcriptome, suggesting the transcriptional machinery governing alternative splicing of Nt(t)PMP3-2 in N. tabacum has conserved origins, derived from a N. tomenosiformis lineage. The above data shows alternative splicing of PMP3 genes contributes to transcript and ORF diversity in plants. All three Nt(t)PMP3-2 splice variants show increased root-specific expression. Implications of Nt(t)PMP3-2 alternative splicing on transcript stability and ORF features are discussed.