Functional analysis of phosphate starvation-regulated protein phosphatase and a general regulation factor (14-3-3) in plants
Abstract
Phosphorus (P) is one of the most important but least available nutrients in the soil. Plants develop a host of morphological, physiological and biochemical adaptations to overcome persistent deficiency of phosphate (Pi). The molecular basis for these adaptations is the coordinated modulation of genes that may involve protein phosphorylation and dephosphorylation. In this study, two gene families involved in protein phosphorylation and dephosphorylation a putative protein phosphatase (PS2) and a plant general regulatory factor (14-3-3), were characterized by using reporter genes (β-glucuronidase and green fluorescent protein) and gene knockout and over-expression lines. The PS2 gene family has high similarity with the members of the HAD (haloacid dehalogenase) and DDDD (4 aspartate) super family of proteins with multiple functions. The family member in tomato (LePS2) is the first putative protein phosphatase gene shown to be regulated by Pi starvation in plants. Temporal and spatial expression of the 3 members of AtPS2 family in Arabidopsis revealed their functional specificity during Pi starvation. The gene expression in the cotyledonary leaves point to their potential role in mobilizing Pi during early seedling development. Altering the expression of PS2 genes resulted in metabolic changes such as altered Pi content, Pi uptake and phosphatase activity, and as well as phenotypic changes during the early growth stages. It also delayed tomato plant maturity and flowering. Considering the potential of PS2 members to function as phosphoprotein phosphatase, any significant alterations in their expression are likely to lead to changes in plant response to Pi deficiency. In contrast to induction of PS2 family members during Pi deficiency, many members of 14-3-3 family were suppressed under Pi limiting conditions. This response is specific and reversible by replenishment of Pi. Several Pi starvation regulated genes contain predicted 14-3-3 binding domain making them as potential targets for post-transcriptional modification. Accumulation of starch, generally observed under Pi deficiency, was suppressed by over-expression of 14-3-3 gene (GRF9) suggesting a negative correlation between gene expression and Pi starvation induced response. The outcome of this research shows that two key molecular determinants, whose expressions are altered under Pi deficiency could play a significant role in plant adaptation to this condition.
Degree
Ph.D.
Advisors
Raghothama, Purdue University.
Subject Area
Molecular biology|Horticulture|Plant propagation
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