ABSTRACT
Pro accumulation in plants is a well-documented physiological response to osmotic stress caused by drought or salinity. In Arabidopsis (Arabidopsis thaliana), the stress and ABA-induced Δ1-PYRROLINE-5-CARBOXYLATE SYNTHETASE1 (P5CS1) gene was previously shown to control Pro biosynthesis in such adverse conditions. To identify regulatory factors that control the transcription of P5CS1, Y1H screens were performed with a genomic fragment of P5CS1, containing 1.2-kB promoter and 0.8-kb transcribed regions. The myeloblastosis (MYB)-type transcription factors PHOSPHATE STARVATION RESPONSE1 (PHR1) and PHR1-LIKE1 (PHL1) were identified to bind to P5CS1 regulatory sequences in the first intron, which carries a conserved PHR1-binding site (P1BS) motif. Binding of PHR1 and PHL1 factors to P1BS was confirmed by Y1H, electrophoretic mobility assay and chromatin immunoprecipitation. Phosphate starvation led to gradual increase in Pro content in wild-type Arabidopsis plants as well as transcriptional activation of P5CS1 and PRO DEHYDROGENASE2 genes. Induction of P5CS1 transcription and Pro accumulation during phosphate deficiency was considerably reduced by phr1 and phl1 mutations and was impaired in the ABA-deficient aba2-3 and ABA-insensitive abi4-1 mutants. Growth and viability of phr1phl1 double mutant was significantly reduced in phosphate-depleted medium, while growth was only marginally affected in the aba2-3 mutants, suggesting that ABA is implicated in growth retardation in such nutritional stress. Our results reveal a previously unknown link between Pro metabolism and phosphate nutrition and show that Pro biosynthesis is target of cross talk between ABA signaling and regulation of phosphate homeostasis through PHR1- and PHL1-mediated transcriptional activation of the P5CS1 gene.
Subject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/genetics , Glutamate-5-Semialdehyde Dehydrogenase/metabolism , Multienzyme Complexes/metabolism , Phosphotransferases (Alcohol Group Acceptor)/metabolism , Proline/metabolism , Signal Transduction , Transcription Factors/metabolism , Abscisic Acid/metabolism , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Binding Sites , Glutamate-5-Semialdehyde Dehydrogenase/genetics , Multienzyme Complexes/genetics , Mutation , Phosphates/deficiency , Phosphotransferases (Alcohol Group Acceptor)/genetics , Plant Growth Regulators/metabolism , Promoter Regions, Genetic/genetics , Pyrroles/metabolism , Transcription Factors/genetics , Transcriptional ActivationABSTRACT
KEY MESSAGE: An unambiguous nomenclature is proposed for the twenty-eight-member LOB domain transcription factor family in Brachypodium . Expression analysis provides unique transcript patterns that are characteristic of a wide range of organs and plant parts. LOB (lateral organ boundaries)-domain proteins define a family of plant-specific transcription factors involved in developmental processes from embryogenesis to seed production. They play a crucial role in shaping the plant architecture through coordinating cell fate at meristem to organ boundaries. Despite their high potential importance, our knowledge of them is limited, especially in the case of monocots. In this study, we characterized LOB domain protein coding genes (LBDs) of Brachypodium distachyon, a model plant for grasses, and present their phylogenetic relationships and an overall spatial expression study. In the Brachypodium genome database, 28 LBDs were found and then classified based on the presence of highly conserved LOB domain motif. Their transcript amounts were measured via quantitative real-time RT-PCR in 37 different plant parts from root tip to generative organs. Comprehensive phylogenetic analysis suggests that there are neither Brachypodium- nor monocot-specific lineages among LBDs, but there are differences in terms of complexity of subclasses between monocots and dicots. Although LBDs in Brachypodium have wide variation of tissue-specific expression and relative transcript levels, overall expression patterns show similarity to their counterparts in other species. The varying transcript profiles we observed support the hypothesis that Brachypodium LBDs have diverse but conserved functions in plant organogenesis.
Subject(s)
Brachypodium/genetics , Multigene Family , Phylogeny , Plant Proteins/genetics , Transcription, Genetic , Amino Acid Sequence , Chromosomes, Plant/genetics , Cluster Analysis , Gene Expression Profiling , Gene Expression Regulation, Plant , Genes, Plant , Plant Proteins/chemistry , Plant Proteins/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , Sequence AlignmentABSTRACT
Greenhouse grown tobacco (Nicotiana tabacum L. cv. Petit Havana) plants were exposed to supplemental UV centred at 318 nm and corresponding to 13.6 kJ m(-2) d(-1) biologically effective UV-B (280-315 nm) radiation. After 6 days this treatment decreased photosynthesis by 30%. Leaves responded by a large increase in UV-absorbing pigment content and antioxidant capacities. UV-stimulated defence against ROS was strongest in chloroplasts, since activities of plastid enzymes FeSOD and APX had larger relative increases than other, non-plastid specific SODs or peroxidases. In addition, non-enzymatic defence against hydroxyl radicals was doubled in UV treated leaves as compared to controls. In UV treated leaves, the extent of activation of ROS neutralizing capacities followed a peroxidases > hydroxyl-radical neutralization > SOD order. These results suggest that highly effective hydrogen peroxide neutralization is the focal point of surviving UV-inducible oxidative stress and argue against a direct signalling role of hydrogen peroxide in maintaining adaptation to UV, at least in laboratory experiments.
