Delayed leaf greening involves a major shift in expression of cytosolic and mitochondrial ribosomes to plastid ribosomes in the highly phosphorus-use-efficient Hakea prostrata (Proteaceae)

Hakea prostrata (Proteaceae) maintains a high photosynthetic rate at low leaf phosphorus and exhibits delayed leaf greening, a convergent adaptation found in many plant families where investment in photosynthetic machinery is delayed until after the leaf structure is built, saving on nutrient investment. To identify the dynamics of gene expression underlying delayed greening, we made a de novo transcriptome assembly for H. prostrata using roots and leaves from hydroponically grown plants, and leaves from five morphologically distinct stages of leaf development from wild plants. Abundance of unique transcripts was compared among the developing leaf stages to identify differentially expressed genes, which were separated into groups based on co-expression patterns. In general, transcripts encoding functions associated with leaf structure decreased in abundance across leaf development, with this concomitant with the decline in foliar P and N concentrations. An enrichment of differentially expressed genes associated with photosynthetic function increased in abundance at or after leaf expansion and much later in development than in species that do not have delayed greening. The abundance of transcripts encoding cytoplasmic and mitochondrial ribosomal subunits generally declined across leaf development, whilst transcripts encoding chloroplast ribosomal subunits increased. Taken together, these results indicate a clear shift in protein synthesis apparatus, moving from a leaf developmental stage and into the photosynthetically-active stage. Gene expression profiling analysis of RNA-seq data for wild growing leaves of Hakea prostrata . We compared expression of genes over four stages of leaf growth, with three replicates per stage.