OsFY, a Homolog of AtFY, Encodes a Protein that Can Interact with OsFCA-γ in Rice （Oryza sativa L.）

FCA and FY are flowering time related genes involved in the autonomous flowering pathwayin Arabidopsis.FCA interacts with FY to regulate the alternative processing of FCA pre-mRNA.The FCA/FY interaction is also required for the regulation of FLC expression,a major floral repressor in Arabidopsis.However,it is not clear if the regulation of this autonomous flowering pathway is also present in monocotplants,such as rice.Recently,alternative RNA processing of OsFCA was observed in rice,which stronglysuggested the existence of an autonomous flowering pathway in rice.In this work,we cloned the cDNA ofthe autonomous flowering pathway gene OsFY from rice.The predicted OsFY protein contained a conserved7 WD-repeat region and at least two Pro-Pro-Leu-Pro motifs compared to Arabidopsis FY.The protein-protein interaction between OsFY and OsFCA-γ,the key feature of their gene function,was also demon-strated using the yeast two-hybrid system.The GenBank database search provided evidence of expressionfor other autonomous pathway gene homologs in rice.These results indicate that the autonomous floweringpathway is present in monocots,and the regulation through FY and FCA interaction is conserved betweenmonocots and dicots.     

The Arabidopsis Spontaneous Cell Death1 gene, encoding a ζ-carotene desaturase essential for carotenoid biosynthesis, is involved in chloroplast development,photoprotection and retrograde signalling

Carotenoids, a class of natural pigments found in all photosynthetic organisms, are involved in a variety of physiological processes, including coloration, photoprotection, biosynthesis of abscisic acid （ABA） and chloroplast biogenesis. Although carotenoid biosynthesis has been well studied biochemically, the genetic basis of the pathway is not well understood. Here, we report the characterization of two allelic Arabidopsis mutants, spontaneous cell death1-1 （spcl-1） and spc1-2. The weak allele spc1-1 mutant showed characteristics of bleached leaves, accumulation of superoxide and mosaic cell death. The strong mutant allele spc1-2 caused a complete arrest of plant growth and development shortly after germination, leading to a seedling-lethal phenotype. Genetic and molecular analyses indicated that SPC1 encodes a putative ζ-carotene desaturase （ZDS） in the carotenoid biosynthesis pathway. Analysis of carotenoids revealed that several major carotenoid compounds downstream of SPC 1/ZDS were substantially reduced in spc1-1, suggesting that SPC 1 is a functional ZDS. Consistent with the downregulated expression of CAO and PORB, the chlorophyll content was decreased in spc1-1 plants. In addition, expression of Lhcb1. 1, Lhcbl. 4 and RbcS was absent in spc1-2, suggesting the possible involvement of carotenoids in the plastid-to-nucleus retrograde signaling. The spc1-1 mutant also displays an ABA-deficient phenotype that can be partially rescued by the externally supplied phytohormone. These results suggest that SPC1/ZDS is essential for biosynthesis of carotenoids and plays a crucial role in plant growth and development.     

Characterization of the Rice Floral Organ Number Mutant fon3

A spontaneous rice mutant named floral organ number 3 (fon3) had major mutations in floral organ numbers. Genetic analysis indicated that fort3 acted as a single recessive gene. Microscopic observation showed that the number of floral organs infon3 increased centripetally. For example, the number of pistils was the more frequently increased than organs in the outer whorls. Homeotic conversion of lodicules and glumes into palea/lemma-like organs was observed in some flowers. Scanning electron microscopy observation showed that the size of flower meristems was maintained the same or similar until the lemma primordium started to differentiate, at which time the floral meristem became enlarged, suggesting abnormal development of the inner whorls of rice florets. The relationship of fort3 with other similar rice mutants is discussed.     

Temporal and Spatial Requirement of EMF1 Activity for Arabidopsis Vegetative and Reproductive Development

EMBRYONIC FLOWER （EMF） genes are required to maintain vegetative development via repression of flower homeotic genes in Arabidopsis. Removal of EMF gene function caused plants to flower upon germination, producing abnormal and sterile flowers. The pleiotropic effect of ernfl mutation suggests its requirement for gene programs involved in diverse developmental processes. Transgenic plants harboring EMF1 promoter：：glucuronidase （GUS） reporter gene were generated to investigate the temporal and spatial expression pattern of EMF1. These plants displayed differential GUS activity in vegetative and flower tissues, consistent with the role of EMF1 in regulating multiple gene programs. EMFI：：GUS expression pattern in emf mutants suggests organ-specific auto-regulation. Sense- and antisense （as） EMF1 cDNA were expressed under the control of stage- and tissue-specific promoters in transgenic plants. Characterization of these transgenic plants showed that EMF1 activity is required in meristematic as well as differentiating tissues to rescue emf mutant phenotype. Temporal removal or reduction of EMF1 activity in the embryo or shoot apex of wild-type seedlings was sufficient to cause early flowering and terminal flower formation in adult plants. Such reproductive cell memory is reflected in the flower MADS-box gene activity expressed prior to flowering in these early flowering plants. However, temporal removal of EMF1 activity in flower meristem did not affect flower development. Our results are consistent with EMF1＇s primary role in repressing flowering in order to allow for vegetative growth.     

Characterization of a novel developmentally retarded mutant (drm1) associated with the autonomous flowering pathway in Arabidopsis

INTRODUCTIONThe transition from vegetative growth to reproductionis one of the most important developmental events in flow-ering plants since it is related to the competence and sur-vivability of a particular species living in a particularenvironment. The…     

Monogenic Recessive Mutations Causing Both Late Floral Initiation and Excess Starch Accumulation in Arabidopsis

A recessive Arabidopsis mutation, carbohydrate accumulation mutant1 (cam1), which maps to position 22.8 on chromosome 3, was identified by screening leaves of ethyl methanesulfonate-mutagenized M2 plants stained with iodine for altered starch content. Increased starch content in leaves of the cam1 mutant was observed at the onset of flowering. This mutant also had a delayed floral initiation phenotype with more rosette leaves than the parental line. In addition, activities of several enzymes associated with starch metabolism were altered in the cam1 mutant. The late-flowering mutant gigantea (gi) also manifested an elevated starch level in leaves. However, not all late-flowering mutants had increased leaf starch content. Double mutants cam1 adg1 (for ADP-glucose pyrophosphorylase), cam1 pgm (for phosphoglucomutase), and gi pgm had no observable starch in leaves but showed the late-flowering phenotype, demonstrating that the elevated starch content is not the cause of late floral initiation. The pleiotropic effects of cam1 and gi suggest that they may play regulatory roles in starch metabolism and floral initiation. These data suggest that starch accumulation and floral initiation may share a common regulatory pathway.     

HUA2 is required for the expression of floral repressors in Arabidopsis thaliana

The HUA2 gene acts as a repressor of floral transition. Lesions in hua2 were identified through a study of natural variation and through two mutant screens. An allele of HUA2 from Landsberg erecta (Ler) contains a premature stop codon and acts as an enhancer of early flowering 4 (elf4) mutants. hua2 single mutants, in the absence of the elf4 lesion, flower earlier than wild type under short days. hua2 mutations partially suppress late flowering in FRIGIDA (FRI )-containing lines, autonomous pathway mutants, and a photoperiod pathway mutant. hua2 mutations suppress late flowering by reducing the expression of several MADS genes that act as floral repressors including FLOWERING LOCUS C (FLC ) and FLOWERING LOCUS M (FLM ).     

Attenuation of brassinosteroid signaling enhances FLC expression and delays flowering

A main developmental switch in the life cycle of a flowering plant is the transition from vegetative to reproductive growth. In Arabidopsis thaliana, distinct genetic pathways regulate the timing of this transition. We report here that brassinosteroid (BR) signaling establishes an unexpected and previously unidentified genetic pathway in the floral-regulating network. We isolated two alleles of brassinosteroid-insensitive 1 (bri1) as enhancers of the late-flowering autonomous-pathway mutant luminidependens (ld). bri1 was found to predominantly function as a flowering-time enhancer. Further analyses of double mutants between bri1 and known flowering-time mutants revealed that bri1 also enhances the phenotype of the autonomous mutant fca and of the dominant FRI line. Moreover, all of these double mutants exhibited elevated expression of the potent floral repressor FLOWERING LOCUS C (FLC). This molecular response could be efficiently suppressed by vernalization, leading to accelerated flowering. Additionally, specific reduction of the expression of FLC via RNA interference accelerated flowering in bri1 ld double mutants. Importantly, combining the BR-deficient mutant cpd with ld also resulted in delayed flowering and led to elevated FLC expression. Finally, we found increased histone H3 acetylation at FLC chromatin in bri1 ld mutants, as compared with ld single mutants. In conclusion, we propose that BR signaling acts to repress FLC expression, particularly in genetic situations, with, for example, dominant FRI alleles or autonomous-pathway mutants, in which FLC is activated.