Table 3.

Genes Implicated in ABA Signaling by Reverse Genetics or Expression Pattern

Locus/Gene	Engineered Effect	Phenotype	Response to ABA	Gene Product	References
AAPK (from Vicia faba)	Dominant   negative	No ABA-induced stomatal closure; no ABA activation of plasma membrane anion channels	Activated	Ser/Thr   protein kinase	Li and Assmann, 1996; Li et al., 2000
AMBP kinase (from Pisum sativum)			Activation; correlated   with stomatal closure   & dehydrin expression	ABA-activated   myelin basic   protein kinase	Burnett et al., 2000
ARSK1			Induced by ABA or NaCl	Root specific   ser/thr kinase	Hwang and Goodman, 1995
ATCDPK1 ATCDPK1a	Constitutively active   mutants expressed   transiently in maize   leaf protoplasts	Constitutive activation of an ABA responsive reporter gene (HVA1-LUC)		Calcium-dependent   protein kinases	Sheen, 1996
AtIP5PII	Overexpression	ABA-insensitive  germination, growth  and gene expression		Inositol   polyphosphate   5-phosphatase II	Sanchez and Chua, 2001
AtPLC1	Antisense suppression	ABA-insensitive germination, growth and gene expression		Phosphoinositide   specific   phospholipase C	Sanchez and Chua, 2001
AtPP2C	Wild-type and mutant proteins expressed transiently in maize leaf protoplasts; antisense suppression	Over-expression blocked ABA-inducible transcription; null mutation had little effect; dominant interfering mutant strongly repressed ABA responses. Antisense conferred increased sensitivity to ABA-induced cold-tolerance and growth inhibition		Protein   phosphatase 2C	Sheen, 1998; Tahtiharju and Palva, 2001
AtRac1/Rop6	Dominant-positive and dominant-negative	Dominant positive blocked ABA-mediated effects on actin cytoskeleton and stomatal closure; dominant negative induced closure in absence of ABA		Small GTPase	Lemichez et al., 2001
			Repressed; correlated with cell division activity	Cyclin-dependent   kinase	Hemerly et al., 1993
GPA1	T-DNA insertion	Increased leaf transpiration; no ABA inhibition of guard cell K+in channels and pH-independent ABA-activation of anion channels		G protein α-subunit	Wang et al., 2001
			Induced by ABA and NaCl; may function in stress response	GSK3/shaggy-like   protein kinase	Piao et al., 1999
			ABA effect unknown; induced by osmotic stress	His kinase   osmosensor	Urao et al., 1999
ICK1			Induced; may suppress cell division	Inhibitor of cyclin- dependent kinase	Wang et al., 1998
MAPKKK			ABA effect unknown; induced by abiotic stresses	Mitogen-activated protein kinase kinase kinase	Mizoguchi et al., 1996
PIP5K			Induced by ABA and abiotic stresses	Phosphatidylinosi-tol-4-phosphate 5-kinase	Mikami et al., 1998
PKABA1	Constitutive expression	Suppression of GA-inducible gene expression in aleurone; small effect on the ABA induction of a LEA gene	Induced	Ser/Thr-protein kinase (from barley)	Gómez-Cadenas et al., 1999
PLDα	Antisense	Decreased ABA and ethylene promotion of senescence		Phospholipase Dα	Fan et al., 1997
ROP2	Dominant negative constitutive	Altered sensitivity to germination inhibition by ABA		Rho-type small GTPase	Li et al., 200
RPK1			Induced by ABA and abiotic stresses; abiotic stress-induction not ABA-dependent	Receptor-like protein kinase	Hong et al., 1997
			Unknown; induced by abiotic stresses	Ribosomal S6 kinase-like	Mizoguchi et al., 1996
WAPK (from tobacco)			Induced	Wounding-induced protein kinase	Lee et al., 1998