Elucidating metabolic and genetic regulators of phosphate uptake and utilisation in brassica

Abstract

Phosphorus (P) is one of the six essential macronutrients in plants. Plants only assimilate P in the form of phosphate (Pi). Plants have developed various adaptations to enhance Pi acquisition and its efficient use. The low availability of Pi in the soil, means many crop plants rely on Pi fertilisers to maintain their growth and development. The overuse of fertilisers pollutes the environment. To overcome this problem, it is crucial to understand the physiological and molecular mechanism of plant Pi uptake and use. Revealing candidate genes underlying trans e-QTL hotspots on chromosome A06 of B. rapa, Phosphate transporter PHO1 (PHO1) genes provide insights on the putative genes which are responsible for Pi transportation and remobilisation in plants. DNA sequencing of five Bacterial Artificial Chromosome (BAC) clones of B. rapa ssp. pekinensis cv. Chiifu revealed the occurrence of four PHO1 paralogues in tandem in the genome sequence. However, only three PHO1 paralogue transcripts could be confirmed by cloning. Membrane lipid remodelling occurred in 24 cultivars of Brassica napus and Brassica rapa R-o-18 photosynthetic membranes under Pi deficient conditions. Plants change their phospholipid compositions to non-phosphorus galactolipid and sulfolipid to release Pi for other cellular functions. Analysis of lipid profiles and expression of lipid metabolism genes in Brassica rapa R-o-18 grown under Pi starvation showed highly responsive lipid metabolism genes are Glycerophosphodiester phosphodiesterase 1 (GDPD1), Monogalactosyldiacylglycerol synthase 3 (MGD3) and Sulfoquinovosyl transferase 2 (SQD2). Analysis of transcript abundance in leaf samples of B. rapa R-o-18 under Pi deficiency through qPCR showed increased transcript abundance for Aluminium activated malate transporter 1 (ALMT) by 7.6-fold, which is involved in organic acid (OA) exudation to improve phosphorus uptake efficiency (PUpE). Whole transcriptome sequencing using RNA-seq revealed 630 transcripts whose expression changed during Pi deficiency across five investigated B. napus lines; 481 genes were upregulated, and 148 genes were down-regulated in response to Pi deficiency. High throughput RNA-seq contributed to molecular identification and regulation underlying biochemical and physiological adaptations to Pi deficiency. These advances provide information of on candidate genes which might be useful in developing future crops with tolerance to low Pi availability.