Visualisation of plastid degradation in sperm cells of wheat pollen

Like most angiosperms, wheat (Triticum aestivum) shows maternal inheritance of plastids. It is thought that this takes place by cytoplasmic stripping at fertilisation rather than the absence of plastids in sperm cells. To determine the fate of plastids during sperm cell development, plastid-targeted green fluorescent protein was used to visualise these organelles in nuclear transgenic wheat lines. Fewer than thirty small 1–2-μm plastids were visible in early uninucleate pollen cells. These dramatically increased to several hundred larger (4 μm) plastids during pollen maturation and went through distinct morphological changes. Only small plastids were visible in generative cells (n = 25) and young sperm cells (n = 9). In mature sperm cells, these green fluorescent protein (GFP)-tagged plastids were absent. This is consistent with maternal inheritance of plastids resulting from their degradation in mature sperm cells in wheat

A 125 kDa RNase E/G-like protein is present in plastids and is essential for chloroplast development and autotrophic growth in Arabidopsis*

Endoribonuclease E (RNase E) is a regulator of global gene expression in Escherichia coli and is the best studied member of the RNase E/G ribonuclease family. Homologues are present in other bacteria but the roles of plant RNase E/G-like proteins are not known. Arabidopsis thaliana contains a single nuclear gene (At2g04270) encoding a product with the conserved catalytic domain of RNase E/G-like proteins. At2g04270 and the adjacent At2g04280 gene form converging transcription units with a ∼40 base overlap at their 3’ ends. Several translation products were predicted from the analyses of At2g04270 cDNAs. An antibody raised against a recombinant A. thaliana RNase E/G-like protein recognized a 125 kDa protein band in purified chloroplast preparations fractionated by SDS-PAGE. The 125 kDa RNase E/G-like protein was detected in cotyledons, rosette and cauline leaves. T-DNA insertions in exon 6 or intron 11 of At2g04270 result in loss of the 125 kDa band or truncation to a 110 kDa band. Loss of At2g04270 function resulted in the arrest of chloroplast development, loss of autotrophic growth, and reduced plastid ribosomal, psbA and rbcL RNA levels. Homozygous mutant plants were pale-green, contained smaller plastids with fewer thylakoids and shorter granal stacks than wild-type chloroplasts, and required sucrose at all growth stages following germination right up to flowering and setting seeds. Recombinant A. thaliana RNase E/G-like proteins rescued an E. coli RNase E mutant and cleaved an rbcL RNA substrate. Expression of At2g04270 was highly correlated with genes encoding plastid polyribonucleotide phosphorylase, S1 RNA-binding, and CRS1/YhbY domain proteins