Knockdown of OsSAE1a affects the growth and development and phosphate homeostasis in rice

SUMOylation is a post-translational modification process that comprises a tandem enzymatic cascade, i.e., maturation, activation, conjugation, and ligation of a small ubiquitin-like modifier, which triggers the modulated activities and transport of the cellular proteins to other areas of the cell. In Oryza sativa (rice), OsSIZ1/2 encoding E3 SUMO ligase exerts regulatory influences on Pi homeostasis and developmental responses. However, the role of OsSAE1a, SUMO E1 activating enzyme, in regulating phosphate (Pi) utilization and/or growth and development is not known in rice and was thus investigated in this study. The qRT-PCR assay revealed a constitutive and variable spatiotemporal expression pattern of OsSAE1a in the vegetative and reproductive tissues and was comparable in the root and shoot grown under different Pi regimes. RNAi-mediated suppression of OsSAE1a exerted variable effects on the concentrations of Pi and total P in different tissues, uptake and distribution of ³²Pi, and relative expression levels of several genes that play pivotal roles in the maintenance of Pi homeostasis. The effects of the mutation in OsSAE1a were also evident in the vegetative and reproductive traits of rice during growth in a hydroponic system and pot soil, respectively. Overall, these results suggest a broad-spectrum role of OsSAE1a in the maintenance of Pi homeostasis and regulating growth and development.

OsPDR2 mediates the regulation on the development response and maintenance of Pi homeostasis in rice

Inorganic orthophosphate (Pi), a major form of essential macronutrient phosphorus (P), is available in rhizosphere for acquisition and assimilation by plants. However, the limited availability of Pi in soils affects the growth and development of plants. In Arabidopsis thaliana (Arabidopsis), Phosphate Deficiency Response2 (AtPDR2), interacts genetically with Low Phosphate Root1 (AtLPR1) in the endoplasmic reticulum (ER) and plays a key role in the inhibition of primary root growth (PRG) during Pi deficiency. However, the role of OsPDR2, the homolog of AtPDR2, either in roots response to Pi deficiency and/or in growth and development has not been elucidated as yet. Therefore, qRT-PCR was employed to determine the spatiotemporal effects and the availability of Pi on the expression of OsPDR2. OsPDR2 showed variable levels of relative expression pattern in vegetative and/or reproductive tissues analyzed at different stages of growth and development (5-17 weeks). Transient expression analysis revealed its subcellular localization to the ER. Further, the reverse genetics approach was employed for determining the function of OsPDR2 by generating RNAi lines (Ri2, Ri9, and Ri18). The study revealed significant inhibitory effects of RNAi-mediated suppression of OsPDR2 on the development of root, male reproductive traits, and yield. Moreover, ³²P isotope labeling and split-root experiments under different Pi regime with RNAi lines revealed the function of OsPDR2 in regulating homeostasis of Pi.