Many plants require circadian clock and light information for the photoperiodic control of flowering. In Arabidopsis, a long-day plant (LDP), flowering is triggered by the circadian clock-controlled expression of CONSTANS (CO) and light stabilization of the CO protein to induce FT (FLOWERING LOCUS T). In rice, a short-day plant (SDP), the CO ortholog Heading date 1 (Hd1) regulates FT ortholog Hd3a, but regulation of Hd3a by Hd1 differs from that in Arabidopsis. Here, we report that phytochrome B (phyB)-mediated suppression of Hd3a is a primary cause of long-day suppression of flowering in rice, based on the three complementary discoveries. First, overexpression of Hd1 causes a delay in flowering under SD conditions and this effect requires phyB, suggesting that light modulates Hd1 control of Hd3a transcription. Second, a single extension of day length decreases Hd3a expression proportionately with the length of daylight. Third, Hd1 protein levels in Hd1-overexpressing plants are not altered in the presence of light. These results also suggest that phyB-mediated suppression of Hd3a expression is a component of the molecular mechanism for critical day length in rice.

Plant grafting is conducted for fruit and vegetable propagation, whereby a piece of living tissue is attached to another through cell-cell adhesion. However, graft compatibility limits combinations to closely related species, and the mechanism is poorly understood. We found that Nicotiana is capable of graft adhesion with a diverse range of angiosperms. Comparative transcriptomic analyses on graft combinations indicated that a subclade of β-1,4-glucanases secreted into the extracellular region facilitates cell wall reconstruction near the graft interface. Grafting was promoted by overexpression of the β-1,4-glucanase. Using Nicotiana stem as an interscion, we produced tomato fruits on rootstocks from other plant families. These findings demonstrate that the process of cell-cell adhesion is a potential target to enhance plant grafting techniques.

Plasticity of root growth in response to environmental cues and stresses is a fundamental characteristic of land plants. However, the molecular basis underlying the regulation of root growth under stressful conditions is poorly understood. Here, we report that a rice nuclear factor, RICE SALT SENSITIVE3 (RSS3), regulates root cell elongation during adaptation to salinity. Loss of function of RSS3 only moderately inhibits cell elongation under normal conditions, but it provokes spontaneous root cell swelling, accompanied by severe root growth inhibition, under saline conditions. RSS3 is preferentially expressed in the root tip and forms a ternary complex with class-C basic helix-loop-helix (bHLH) transcription factors and JASMONATE ZIM-DOMAIN proteins, the latter of which are the key regulators of jasmonate (JA) signaling. The mutated protein arising from the rss3 allele fails to interact with bHLH factors, and the expression of a significant portion of JAresponsive genes is upregulated in rss3. These results, together with the known roles of JAs in root growth regulation, suggest that RSS3 modulates the expression of JA-responsive genes and plays a crucial role in a mechanism that sustains root cell elongation at appropriate rates under stressful conditions.

The plant hormone jasmonate and its conjugates (JAs) have important roles in growth control, leaf senescence and defense responses against insects and microbial attacks. JA biosynthesis is induced by several stresses, including mechanical wounding, pathogen attacks, drought and salinity stresses. However, the roles of JAs under abiotic stress conditions are unclear. Here we report that increased expression of the Cyt P450 family gene CYP94C2b enhanced viability of rice plants under saline conditions. This gene encodes an enzyme closely related to CYP94C1 that catalyzes conversion of bioactive jasmonate-isoleucine (JA-Ile) into 12OH-JA-Ile and 12COOH-JA-Ile. Inactivation of JA was facilitated in a rice line with enhanced CYP94C2b expression, and responses to exogenous JA and wounding were alleviated. Moreover, salt stress-induced leaf senescence but not natural senescence was delayed in the transgenic rice. These results suggest that bioactive JAs have a negative effect on viability under salt stress conditions and demonstrate that manipulating JA metabolism confers enhanced salt tolerance in rice.

Tissue adhesion between plant species occurs both naturally and artificially. Parasitic plants establish intimate relationship with host plants by adhering tissues at roots or stems. Plant grafting, on the other hand, is a widely used technique in agriculture to adhere tissues of two stems. Here we found that the model Orobanchaceae parasitic plant Phtheirospermum japonicum can be grafted on to interfamily species. To understand molecular basis of tissue adhesion between distant plant species, we conducted comparative transcriptome analyses on both infection and grafting by P. japonicum on Arabidopsis . Despite different organs, we identified the shared gene expression profile, where cell proliferation- and cell wall modification-related genes are up-regulated. Among genes commonly induced in tissue adhesion between distant species, we showed a gene encoding a secreted type of β-1,4-glucanase plays an important role for plant parasitism. Our data provide insights into the molecular commonality between parasitism and grafting in plants.

No abstract

In a determinate meristem, such as a floral meristem, a genetically determined number of organs are produced before the meristem is terminated. In rice, iterative formation of organs during flower development with defects in meristem determinacy, classically called 'proliferation', is caused by several mutations and observed in dependence on environmental conditions. Here we report that overexpression of several JAZ proteins, key factors in jasmonate signaling, with mutations in the Jas domains causes an increase in the numbers of organs in florets, aberrant patterns of organ formation and repetitious organ production in spikelets. Our results imply that JAZ factors modulate mechanisms that regulate meristem functions during spikelet development.Meristems provide cells that differentiate and produce organs to sustain plant growth. In indeterminate meristems, such as vegetative and inflorescence meristems, meristematic activity is maintained by continuous cell proliferation balanced with cell differentiation. By contrast in determinate meristems, such as floral meristems, meristematic activity ceases after initiation of a certain number of organs. In general, floral meristem determinacy is regulated genetically. In Arabidopsis, for example, AGA-MOUS has a role in repression of WUSCHEL that is required for maintenance of stem cells in the meristem during flower development (for a review see ref. 1). Strong agamous mutant alleles develop a set of floral organs (sepals-petals-petals) repeatedly, instead of carpel formation, reflecting prolonged maintenance of an active meristem at the center of the flower.1 In rice, flower development occurs in a spikelet, a special inflorescence unit, which produces 2 rudimentary glumes and 2 sterile lemmas and a floret that comprises floral organs (pistil, stamen and lodicule) and outer organs (palea and lemma) (for reviews see refs. 2-3). Determinacy of the floral meristem in rice is controlled by OsMADS58, 4 whereas determinacy of the spikelet meristem and transition of the spikelet meristem to the floral meristem is regulated by OsMADS1/LEAFY HULL STERILE1 (LHS1).3,5 Indeterminate development of flowers consisting of lodicules, stamens and caperl-like organ, but not palea and lemma, was caused by RNA siliencing of OsMADS58. 4 In lhs1 mutants, an additional flower generation in a floret and repetitious formation of leaf-like paleae and lemmas within a spikelet is often observed. 2,5In rice, various types of abnormal spikelet development are induced by cold weather. These include an increase in the number of spikelet organs and formation of multiple-floret spikelets. 6 Moreover, findings of 'proliferated propagule spikelet' formation has been reported in a field survey of cold damages and is characterized by development of foliaceous glumes and leaves in a spikelet, 6 resembling the phenotype observed in lhs1 as described above. Takeoka and Shimizu (1973) 7 reported similar defects in a rice mutant where repetitious formation of vegetative organs ('leafy-shoot-type proliferation'...

Flagellin is a component of bacterial flagella and acts as a proteinaceous elicitor of defence responses in organisms. Flagellin from a phytopathogenic bacterium, Acidovorax avenae strain N1141, induces immune responses in suspension-cultured rice cells. To analyse the function of flagellin in rice, we fused the N1141 flagellin gene to the cauliflower mosaic virus 35S promoter and introduced it into rice. Many of the resulting transgenic rice plants accumulated flagellin at various levels. The transgenic rice developed pale spots in the leaves. The expression of a defence-related gene for phenylalanine ammonia-lyase was induced in the transgenic plants, and H(2)O(2) production and cell death were observed in some plants with high levels of gene expression, suggesting that the flagellin triggers immune responses in the transgenic rice. Transgenic plants inoculated with Magnaporthe grisea, the causal agent of rice blast, showed enhanced resistance to blast, suggesting that the flagellin production confers disease resistance in the transgenic rice.