TAP46 Plays a Positive Role in the ABSCISIC ACID INSENSITIVE5-Regulated Gene Expression in Arabidopsis    

Abstract

TAP46 is a protein phosphatase2A (PP2A)-associated protein that regulates PP2A activity in Arabidopsis (Arabidopsis thaliana). To study how PP2A is involved in abscisic acid (ABA) signaling in plants, we studied the function of TAP46 in ABA-regulated seed maturation and seedling development. Expression of TAP46 coincides with the action of ABA in developing seeds and during seed germination, and the TAP46 transcript reaches to the highest level in mature seeds. Real-time polymerase chain reaction analysis indicates that external ABA can increase TAP46 transcript level transiently during seed germination. Overexpression of TAP46 increases plant sensitivity to ABA, while tap46 knockdown mutants are less sensitive to ABA during seed germination, suggesting that TAP46 functions positively in ABA signaling. Overexpression of TAP46 also leads to lower PP2A activity, while tap46-1 knockdown mutant displays higher PP2A activity, suggesting that TAP46 negatively regulates PP2A activity in Arabidopsis. Both TAP46 and PP2A interact with the ABA-regulated transcription factor ABA INSENSITIVE5 (ABI5) in vivo, and TAP46's binding to ABI5 can stabilize ABI5. Furthermore, TAP46's binding to the phosphorylated ABI5 may prevent PP2A or PP2A-like protein phosphatases from removing the phosphate from ABI5, thereby maintaining ABI5 in its active form. Overexpression of TAP46 and inhibition of activities of PP2A or PP2A-like protein phosphatases can increase transcript levels of several ABI5-regulated genes, suggesting that TAP46 is a positive factor in the ABA-regulated gene expression in Arabidopsis.

Identification of Open Stomata1-Interacting Proteins Reveals Interactions with Sucrose Non-fermenting1-Related Protein Kinases2 and with Type 2A Protein Phosphatases That Function in Abscisic Acid Responses

“…Future analyses will require investigations of SnRK2-type protein kinase activities in higher order pp2a mutants and in specific tissues and cell types and activity measurements of PP2A-type protein phosphatases after prolonged ABA treatments. Note that a 1-d ABA treatment drastically reduced PP2A-type phosphatase activity in germinating seeds (Hu et al, 2014).…”

“…Differences between ABA responses in Ws and Col-0 may result from altered expression levels between natural accessions of Arabidopsis. For instance, PP2A-type protein phosphatase activity in Ws was 4-fold higher compared with that in Col-0 (Hu et al, 2014). Gene dosages of regulatory PP2AA subunits were discussed to be important for PP2A-type protein phosphatase function (DeLong, 2006).…”

Arabidopsis PHOSPHOTYROSYL PHOSPHATASE ACTIVATOR Is Essential for PROTEIN PHOSPHATASE 2A Holoenzyme Assembly and Plays Important Roles in Hormone Signaling, Salt Stress Response, and Plant Development

“…These results showed that while the expression of ABI5 transcripts was not affected in amiR plants, ABI5-regulated gene expression was increased. Since PP2A negatively regulates ABI5 activity (Hu et al, 2014), these results could be interpreted to indicate that reduced PP2A activity in amiR plants may be responsible for the increased expression of ABI5 downstream genes.…”

“…The response of amiR plants to cantharidin, an inhibitor of PP2A and PP2A-related phosphatases such as PP6 (Li and Casida, 1992;Hu et al, 2014), was also analyzed. Four-day-old seedlings were transferred to MS plates that were not supplemented or were supplemented with 10 mM cantharidin, and plants were allowed to grow for an additional 4 d before the main root length was measured.…”

“…It was reported that ABI5, a transcriptional factor that was negatively regulated by PP2A, could be detected at both seed and seedling stages (Lopez-Molina et al, 2001;Liu and Stone, 2010;Hu et al, 2014). Therefore, we measured the transcript of ABI5 and several ABI5-regulated Figure 4.…”