BackgroundRice zebra mutants are leaf variegation mutants that exhibit transverse sectors of green/yellow or green/white in developing or mature leaves. In most cases, leaf variegation is caused by defects in chloroplast biogenesis pathways, leading to an accumulation of reactive oxygen species in a transverse pattern in the leaves. Here, we examine a new type of leaf variegation mutant in rice, zebra3 (z3), which exhibits transverse dark-green/green sectors in mature leaves and lacks the typical yellow or white sectors.ResultsMap-based cloning revealed that the Z3 locus encodes a putative citrate transporter that belongs to the citrate-metal hydrogen symport (CitMHS) family. CitMHS family members have been extensively studied in bacteria and function as secondary transporters that can transport metal-citrate complexes, but whether CitMHS family transporters exist in eukaryotes remains unknown. To investigate whether Z3 acts as a citrate transporter in rice, we measured citrate levels in wild-type leaves and in the dark-green and green sectors of the leaves of z3 mutants. The results showed that citrates accumulated to high levels in the dark-green sectors of z3 mutant leaves, but not in the green sectors as compared with the wild-type leaves.ConclusionsThese results suggest that leaf variegation in the z3 mutant is caused by an unbalanced accumulation of citrate in a transverse pattern in the leaves. Taking these results together, we propose that Z3 plays an important role in citrate transport and distribution during leaf development and is a possible candidate for a CitMHS family member in plants.Electronic supplementary materialThe online version of this article (10.1186/s12284-017-0196-8) contains supplementary material, which is available to authorized users.

BackgroundNADPH: protochlorophyllide oxidoreductase (POR) is an essential enzyme that catalyzes the photoreduction of protochlorophyllide to chlorophyllide, which is ultimately converted to chlorophyll in developing leaves. Rice has two POR isoforms, OsPORA and OsPORB. OsPORA is expressed in the dark during early leaf development; OsPORB is expressed throughout leaf development regardless of light conditions. The faded green leaf (fgl) is a loss-of-function osporB mutant that displays necrotic lesions and variegation in the leaves due to destabilized grana thylakoids, and has increased numbers of plastoglobules in the chloroplasts. To investigate whether the function of OsPORA can complement that of OsPORB, we constitutively overexpressed OsPORA in fgl mutant.ResultsIn the 35S:OsPORA/fgl (termed OPAO) transgenic plants, the necrotic lesions of the mutant disappeared and the levels of photosynthetic pigments and proteins, as well as plastid structure, were recovered in developing leaves under natural long days in the paddy field and under short days in an artificially controlled growth room. Under constant light conditions, however, total chlorophyll and carotenoid levels in the developing leaves of OPAO plants were lower than those of wild type. Moreover, the OPAO plants exhibited mild defects in mature leaves beginning at the early reproductive stage in the paddy field.ConclusionsThe physiological function of OsPORB in response to constant light or during reproductive growth cannot be completely replaced by constitutive activity of OsPORA, although the biochemical functions of OsPORA and OsPORB are redundant. Therefore, we suggest that the two OsPORs have differentiated over the course of evolution, playing distinct roles in the adaptation of rice to the environment.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-016-0141-2) contains supplementary material, which is available to authorized users.

Lesion mimic mutants (LMMs) are usually controlled by single recessive mutations that cause the formation of necrotic lesions without pathogen invasion. These genetic defects are useful to reveal the regulatory mechanisms of defense-related programmed cell death in plants. Molecular evidence has been suggested that some of LMMs are closely associated with the regulation of leaf senescence in rice (Oryza sativa). Here, we characterized the mutation underlying spotted leaf4 (spl4), which results in lesion formation and also affects leaf senescence in rice. Map-based cloning revealed that the γ ray-induced spl4-1 mutant has a single base substitution in the splicing site of the SPL4 locus, resulting in a 13-bp deletion within the encoded microtubule-interacting-and-transport (MIT) spastin protein containing an AAA-type ATPase domain. The T-DNA insertion spl4-2 mutant exhibited spontaneous lesions similar to those of the spl4-1 mutant, confirming that SPL4 is responsible for the LMM phenotype. In addition, both spl4 mutants exhibited delayed leaf yellowing during dark-induced or natural senescence. Western blot analysis of spl4 mutant leaves suggested possible roles for SPL4 in the degradation of photosynthetic proteins. Punctate signals of SPL4-fused fluorescent proteins were detected in the cytoplasm, similar to the cellular localization of animal spastin. Based on these findings, we propose that SPL4 is a plant spastin that is involved in multiple aspects of leaf development, including senescence.

The WRKY family of transcription factors plays a pivotal role in plant responses to biotic and abiotic stress. The WRKY Group III transcription factor OsWRKY114 is a positive regulator of innate immunity against Xanthomonas oryzae pv. oryzae; however, its role in abiotic stress responses is largely unknown. In this study, we showed that the abundant OsWRKY114 transcripts present in transgenic rice plants are reduced under drought conditions. The overexpression of OsWRKY114 significantly increased drought sensitivity in rice, which resulted in a lower survival rate after drought stress. Moreover, we showed that stomatal closure, which is a strategy to save water under drought, is restricted in OsWRKY114-overexpressing plants compared with wild-type plants. The expression levels of PYR/PYL/RCAR genes, such as OsPYL2 and OsPYL10 that confer drought tolerance through stomatal closure, were also markedly lower in the OsWRKY114-overexpressing plants. Taken together, these results suggest that OsWRKY114 negatively regulates plant tolerance of drought stress via inhibition of stomatal closure, which would otherwise prevent water loss in rice.

No abstract