Phosphate deficiency responsive TaSPX3 is involved in the regulation of shoot phosphorus in Arabidopsis plants.

SPX (SYG/PHO81/XPR1) domain genes have been reported to play vital roles in the Phosphorus (Pi) signaling network in Arabidopsis thaliana and rice. However, the functions of SPX proteins in wheat remain largely unknown. In this study, the full-length cDNA sequence of the TaSPX3 gene was cloned from the common wheat variety Zhengmai9023. The expression of TaSPX3 was up-regulated in eight different genotypes of wheat under low phosphorus (LP) stress, indicating that TaSPX3 responds to Pi limitation in multiple wheat genotypes. The transcription level of TaSPX3 was also detected in the absence of seven different elements, showing certain specificity for Pi deficiency in wheat. Over expressing TaSPX3 in Arabidopsis can alleviate Pi deficiency symptoms at the seedling stage and promote the growth of plant, and advance the flowering period at the adult stage. The expression of 7 genes associated with the Pi starvation signal pathways was analyzed using qRT-PCR. The results showed that TaSPX3, along with AtSPX1, AtRNS1, AtIPS1, AtPAP2, AtPAP17 and AtAT4, were all induced by Pi deficiency. This study reveals that the TaSPX3 gene in wheat is involved in the response to phosphorus stress and may affect shoot phosphorus levels through AT4 or PAPs-related pathways. Overall, our study provides new insights into the regulation of plant response under LP conditions and the molecular mechanism underlying the role of the wheat SPX gene in coping with LP stress.

Cytochrome P450 promiscuity leads to a bifurcating biosynthetic pathway for tanshinones.

Cytochromes P450 (CYPs) play a key role in generating the structural diversity of terpenoids, the largest group of plant natural products. However, functional characterization of CYPs has been challenging because of the expansive families found in plant genomes, diverse reactivity and inaccessibility of their substrates and products. Here we present the characterization of two CYPs, CYP76AH3 and CYP76AK1, which act sequentially to form a bifurcating pathway for the biosynthesis of tanshinones, the oxygenated diterpenoids from the Chinese medicinal plant Danshen (Salvia miltiorrhiza). These CYPs had similar transcription profiles to that of the known gene responsible for tanshinone production in elicited Danshen hairy roots. Biochemical and RNA interference studies demonstrated that both CYPs are promiscuous. CYP76AH3 oxidizes ferruginol at two different carbon centers, and CYP76AK1 hydroxylates C-20 of two of the resulting intermediates. Together, these convert ferruginol into 11,20-dihydroxy ferruginol and 11,20-dihydroxy sugiol en route to tanshinones. Moreover, we demonstrated the utility of these CYPs by engineering yeast for heterologous production of six oxygenated diterpenoids, which in turn enabled structural characterization of three novel compounds produced by CYP-mediated oxidation. Our results highlight the incorporation of multiple CYPs into diterpenoid metabolic engineering, and a continuing trend of CYP promiscuity generating complex networks in terpenoid biosynthesis.