Exon-intron architecture and chromosomal location of PLD genes in Arabidopsis. White boxes represent coding sequences. Yellow boxes delimit un-translated regions revealed by cDNA and/or EST sequences. Blue areas in AtPLDy2 and AtPLDδ indicate potential alternative splicing (see the text). Orange regions in AtPLDβ1 and AtPLDβ2 indicate the portion of the first exon coding for the unusual N-terminal extension (details in the text). Note the three basic types of gene organisation. Black arrowheads indicate positions of introns presumably lost from the AtPLDp2 gene (compare to AtPLDp1). The inset shows locations of the PLD genes on the Arabidopsis chromosomes.