Zhenbiao Yang — Page 2

PubMed2002

Plasma membrane-associated ROP10 small GTPase is a specific negative regulator of abscisic acid responses in Arabidopsis.

Abscisic acid (ABA) is an important plant hormone that modulates seed germination and plant growth and stress responses, but its signaling remains poorly understood. We investigated the role of ROP10, a member of the Arabidopsis Rop subfamily of Rho GTPases, in ABA signaling. A null rop10 mutant exhibits enhanced responses to ABA in seed germination, root elongation, and stomatal closure assays and in the induction of expression of the transcription factor MYB2, but it shows wild-type levels of ABA and normal responses to other hormones. Consistently, transgenic expression of a constitutively active form of ROP10 reduces ABA inhibition of seed germination, whereas dominant-negative mutants of ROP10 enhance ABA response and partially suppress abi2. Furthermore, ABA specifically downregulates ROP10 transcription in root tips. ROP10 is localized to the plasma membrane (PM), and PM localization is crucial for its function. These results suggest that ROP10 is a PM-localized signaling molecule that is involved specifically in the negative regulation of ABA signaling.

Abscisic Acid↗

PubMed2002

The Arabidopsis Rop2 GTPase is a positive regulator of both root hair initiation and tip growth.

Root hairs provide a model system for the study of cell polarity. We examined the possibility that one or more members of the distinct plant subfamily of RHO monomeric GTPases, termed Rop, may function as molecular switches regulating root hair growth. Specific Rops are known to control polar growth in pollen tubes. Overexpressing Rop2 (Rop2 OX) resulted in a strong root hair phenotype, whereas overexpressing Rop7 appeared to inhibit root hair tip growth. Overexpressing Rops from other phylogenetic subgroups of Rop did not give a root hair phenotype. We confirmed that Rop2 was expressed throughout hair development. Rop2 OX and constitutively active GTP-bound rop2 (CA-rop2) led to additional and misplaced hairs on the cell surface as well as longer hairs. Furthermore, CA-rop2 depolarized root hair tip growth, whereas Rop2 OX resulted in hairs with multiple tips. Dominant negative GDP-bound Rop2 reduced the number of hair-forming sites and led to shorter and wavy hairs. Green fluorescent protein-Rop2 localized to the future site of hair formation well before swelling formation and to the tip throughout hair development. We conclude that the Arabidopsis Rop2 GTPase acts as a positive regulatory switch in the earliest visible stage in hair development, swelling formation, and in tip growth.

Actins↗