Two NADPH: Protochlorophyllide Oxidoreductase (POR) Isoforms Play Distinct Roles in Environmental Adaptation in Rice

Kwon, Choon-Tak,Kim, Suk-Hwan,Song, Giha,Kim, Dami,Paek, Nam-Chon Springer US 2017 Rice Vol.10 No.-

<P><B>Background</B></P><P>NADPH: 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. <I>OsPORA</I> is expressed in the dark during early leaf development; <I>OsPORB</I> is expressed throughout leaf development regardless of light conditions. The <I>faded green leaf</I> (<I>fgl</I>) is a loss-of-function <I>osporB</I> 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 <I>OsPORA</I> in <I>fgl</I> mutant.</P><P><B>Results</B></P><P>In the <I>35S:OsPORA/fgl</I> (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.</P><P><B>Conclusions</B></P><P>The 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.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s12284-016-0141-2) contains supplementary material, which is available to authorized users.</P>

Customizing Solanaceae Plants for Vertical Farming by Genome Editing

Choon-Tak Kwon 한국원예학회 2022 한국원예학회 학술발표요지 Vol.2022 No.5

Natural variation in Early flowering1 (EL1) contributes to alteration of heading date and gibberellin signaling in rice

Choon-Tak Kwon,Sung-Hwan Cho,Bon-Hyuk Koo,Soo-Cheul Yoo,Nam-Chon Paek 한국육종학회 2012 한국육종학회 심포지엄 Vol.2012 No.07

The timing of flowering, which is of crucial importance for plant growth and survival, is controlled by intricate pathways. To identify heading date-QTL, we constructed high resolution map on chromosome 3 using heterogeneous inbred family-near isogenic lines (H-NILs) derived from F7 RILs generated by the cross of early-heading japonica rice ‘H143’ and middle-late-heading indica-japonica hybrid cultivar ‘Milyang23’. QTL and subsequent sequence analysis using H-NILs revealed that the gene underlining QTL EH3, which is detected in the region of Hd16, is EL1 encoding casein kinase I (CKI). Two types of single amino acid substitutions in Ser/Thr kinase domain of EL1 were found in various cultivars, among which H-NIL(eh3) caused loss of function in EL1 demonstrated by altered heading date and GA response. Moreover, the phosphorylation of EL1 appears to involve in EL1 activity to regulate heading date. Transcriptional analysis clearly indicated that H-NIL(EH3) suppresses heading under LD conditions by down-regulating Ehd1, there by Hd3a and RFT1 expressions were not induced, suggesting that EL1 is photoperiod-sensitive and functions as a LD-specific suppressor of heading. Further characterization suggested that EL1 is likely to involve in anther development and seed settings by regulating GAMYB expression. Our study demonstrated that the genetic basis of natural variation occurred in ‘H143’ was revealed by QTL analysis using H-NILs, and EH3/EL1 function is crucial for heading and development in rice. The genetic natural variation of H-NIL(eh3) may have contributed to adaptation of rice cultivation to the higher regions by regulating the expression of rice flowering activator genes and GA signaling.

The Rice Floral Repressor <i>Early flowering1</i> Affects Spikelet Fertility By Modulating Gibberellin Signaling

Kwon, Choon-Tak,Kim, Suk-Hwan,Kim, Dami,Paek, Nam-Chon Springer US 2015 Rice Vol.8 No.-

<P><B>Background</B></P><P>Gibberellic acid (GA; or gibberellin) affects the development of floral organs, especially anthers and pollen, and perturbation of development of male floral organs can cause sterility. Many studies of GA signaling have concentrated on anther development, but the effect of GA on grain production remains to be examined.</P><P><B>Results</B></P><P>Using a cross of ‘Milyang23 (M23)’, which has a functional allele of <I>Early flowering1</I> (<I>EL1</I>), and ‘H143’, which has a nonfunctional <I>el1</I> allele, we generated heterogeneous inbred family-near isogenic lines (HNILs) that are homozygous for <I>EL1</I> [HNIL(M23)] or <I>el1</I> [HNIL(H143)]. Here, we found that HNIL(H143) exhibited anther deformities and low pollen viability. The expression of <I>GAMYB</I>, a major activator of GA signaling, and its downstream genes <I>CYP703A3</I> and <I>KAR</I>, mainly involved in pollen formation, increased abnormally during spikelet development; this activation of GA signaling may cause the sterility. To confirm the negative effect of the <I>el1</I> mutation on spikelet fertility, we examined a line carrying a T-DNA insertion <I>el1</I> mutant [hereafter ZH11(<I>el1</I>)] and its parental cultivar ‘Zhonghua11 (ZH11)’. ZH11(<I>el1</I>) showed nearly identical defects in anther development and pollen viability as HNIL(H143), leading to decreased seed setting rate. However, the elite <I>japonica</I> cultivar Koshihikari, which has a nonfunctional <I>el1</I> allele for early flowering in long days, produces fertile spikelets and normal grain yields, like other elite <I>japonica</I> cultivars. This indicates that as-yet-unknown regulator(s) that can overcome the male sterile phenotype of the <I>el1</I> mutation must have been introduced into Koshihikari.</P><P><B>Conclusions</B></P><P>The <I>el1</I> mutation contributes to early flowering in <I>japonica</I> rice under long days but fails to limit GA signaling, thus negatively affecting spikelet fertility, which results in a loss of grain yield. Thus, <I>EL1</I> is essential for photoperiod sensitivity in flowering as well as spikelet fertility in grain production.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s12284-015-0058-1) contains supplementary material, which is available to authorized users.</P>

Functional deficiency of phytochrome B improves salt tolerance in rice

Kwon, Choon-Tak,Song, Giha,Kim, Suk-Hwan,Han, Jaehyuk,Yoo, Soo-Cheul,An, Gynheung,Kang, Kiyoon,Paek, Nam-Chon Elsevier 2018 Environmental and experimental botany Vol.148 No.-

<P><B>Abstract</B></P> <P>Soil degradation affects agriculture worldwide. Soils with high salt can result from local geological conditions or accumulation of salt from irrigation. Salt limits water uptake and reduces crop yields; therefore, salt tolerance is an important trait for crops grown in high-salt soils. Here, we show that the rice (<I>Oryza sativa</I>) <I>phytochrome B</I> (<I>osphyB</I>) mutant has greater tolerance to salt stress than its parent <I>japonica</I> rice (cv. Dongjin). We found that the <I>osphyB</I> mutant showed a higher survival rate, fresh weight, and levels of total chlorophylls and carotenoids, as well as enhanced membrane integrity under salt stress compared to the wild type. <I>OsPHYB</I> transcripts increased in tissues of the wild type after salt treatment; <I>OsPHYB</I> expression was much higher in the leaf blade than in the stem and root. The <I>osphyB</I> mutant accumulated less Na<SUP>+</SUP> in the shoot and considerably more K<SUP>+</SUP> in both the shoot and root, maintaining a significantly lower Na<SUP>+</SUP> to K<SUP>+</SUP> ratio, possibly due to a lower rate of Na<SUP>+</SUP> uptake and a higher rate of K<SUP>+</SUP> uptake. To elucidate the possible mechanism of salt tolerance in the <I>osphyB</I> mutant, we performed quantitative reverse transcription PCR analysis, which indicated that salt stress-associated genes, including transcription factors and high-affinity K<SUP>+</SUP> transporters, are upregulated in the <I>osphyB</I> mutant under high-salinity conditions. Taken together, our findings show that the null mutation of <I>OsPHYB</I> contributes to a decrease in the Na<SUP>+</SUP>/K<SUP>+</SUP> ratio and enhances cell membrane integrity through upregulation of salt stress-associated genes, resulting in improved tolerance to salt stress.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The rice <I>osphyB</I> mutation confers enhanced tolerance to salt stress. </LI> <LI> <I>OsphyB</I> mutants show altered expression of salinity stress-associated genes. </LI> <LI> Altered expression of K<SUP>+</SUP> transporters decreases the Na<SUP>+</SUP>/K<SUP>+</SUP> ratio in <I>osphyB</I> mutants. </LI> <LI> Improved reactive oxygen species scavenging mitigates oxidative stress in <I>osphyB</I>. </LI> </UL> </P>

Gibberellic Acid: A Key Phytohormone for Spikelet Fertility in Rice Grain Production

Kwon, Choon-Tak,Paek, Nam-Chon MDPI 2016 INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES Vol.17 No.5

<P>The phytohormone gibberellic acid (GA) has essential signaling functions in multiple processes during plant development. In the “Green Revolution”, breeders developed high-yield rice cultivars that exhibited both semi-dwarfism and altered GA responses, thus improving grain production. Most studies of GA have concentrated on germination and cell elongation, but GA also has a pivotal role in floral organ development, particularly in stamen/anther formation. In rice, GA signaling plays an important role in spikelet fertility; however, the molecular genetic and biochemical mechanisms of GA in male fertility remain largely unknown. Here, we review recent progress in understanding the network of GA signaling and its connection with spikelet fertility, which is tightly associated with grain productivity in cereal crops.</P>

Casein Kinases I and 2α Phosphorylate Oryza Sativa Pseudo-Response Regulator 37 (OsPRR37) in Photoperiodic Flowering in Rice

Kwon, Choon-Tak,Koo, Bon-Hyuk,Kim, Dami,Yoo, Soo-Cheul,Paek, Nam-Chon Korean Society for Molecular and Cellular Biology 2015 Molecules and cells Vol.38 No.1

Flowering time (or heading date) is controlled by intrinsic genetic programs in response to environmental cues, such as photoperiod and temperature. Rice, a facultative short-day (SD) plant, flowers early in SD and late in long-day (LD) conditions. Casein kinases (CKs) generally act as positive regulators in many signaling pathways in plants. In rice, Heading date 6 (Hd6) and Hd16 encode $CK2{\alpha}$ and CKI, respectively, and mainly function to delay flowering time. Additionally, the major LD-dependent floral repressors Hd2/Oryza sativa Pseudo-Response Regulator 37 (OsPRR37;hereafter PRR37) and Ghd7 also confer strong photoperiod sensitivity. In floral induction, Hd16 acts upstream of Ghd7 and CKI interacts with and phosphorylates Ghd7. In addition, Hd6 and Hd16 also act upstream of Hd2. However, whether CKI and $CK2{\alpha}$ directly regulate the function of PRR37 remains unclear. Here, we use in vitro pull-down and in vivo bimolecular fluorescence complementation assays to show that CKI and $CK2{\alpha}$ interact with PRR37. We further use in vitro kinase assays to show that CKI and $CK2{\alpha}$ phosphorylate different regions of PRR37. Our results indicate that direct posttranslational modification of PRR37 mediates the genetic interactions between these two protein kinases and PRR37. The significance of CK-mediated phosphorylation for PRR37 and Ghd7 function is discussed.

Leaf variegation in the rice zebra2 mutant is caused by photoperiodic accumulation of tetra-cis-lycopene and singlet oxygen

Su-Hyun Han,Choon-Tak Kwon,Yasuhito Sakuraba,Nam-Chon Paek 한국육종학회 2012 한국육종학회 심포지엄 Vol.2012 No.07

In field conditions, the zebra2 (z2) mutant in rice (Oryza sativa) produces leaves with transverse pale-green/yellow stripes. It was recently reported that ZEBRA2 encodes carotenoid isomerase (CRTISO) and that low levels of lutein, an essential carotenoid for non-photochemical quenching, cause leaf variegation in z2 mutants. However, we found that the z2 mutant phenotype was completely suppressed by growth under continuous light (CL; permissive) conditions, with concentrations of chlorophyll, carotenoids and chloroplast proteins at normal levels in z2 mutants under CL. In addition, three types of reactive oxygen species (ROS; superoxide [O2-], hydrogen peroxide [H2O2], and singlet oxygen [1O2]) accumulated to high levels in z2 mutants grown under short-day conditions (SD; alternate 10-h light/14-h dark; restrictive), but do not accumulate under CL conditions. However, the levels of lutein and zeaxanthin in z2 leaves were much lower than normal in both permissive CL and restrictive SD growth conditions, indicating that deficiency of these two carotenoids is not responsible for the leaf variegation phenotype. We found that the CRTISO substrate tetra-cis-lycopene accumulated during the dark periods under SD, but not under CL conditions. Its accumulation was also positively correlated with 1O2 levels generated during the light period, which consequently altered the expression of 1O2-responsive and cell death-related genes in the variegated z2 leaves. Taking these results together, we propose that the z2 leaf variegation can be largely attributed to photoperiodic accumulation of tetra-cis-lycopene and generation of excessive 1O2 under natural day-night conditions.

Natural Variation in OsPRR37 Regulates Heading Date and Contributes to Rice Cultivation at a Wide Range of Latitudes

Soo-Cheul Yoo,Bon-Hyuk Koo,Choon-Tak Kwon,Nam-Chon Paek 한국육종학회 2014 한국육종학회 심포지엄 Vol.2014 No.07

Heading date and photoperiod sensitivity are fundamental traits that determine rice adaptation to a wide range of geographic environments. By quantitative trait locus (QTL) mapping and candidate gene analysis using wholegenome re-sequencing, we found that Oryza sativa Pseudo-Response Regulator37 (OsPRR37; hereafter PRR37) is responsible for the Early heading7-2 (EH7-2)/Heading date2 (Hd2) QTL which was identified from a cross of late-heading rice ‘Milyang23 (M23)’ and early-heading rice ‘H143’. H143 contains a missense mutation of an invariantly conserved amino acid in the CCT (CONSTANS, CO-like, and TOC1) domain of PRR37 protein. In the world rice collection, different types of nonfunctional PRR37 alleles were found in many European and Asian rice cultivars. Notably, the japonica varieties harboring nonfunctional alleles of both Ghd7/Hd4 and PRR37/Hd2 flower extremely early under natural long-day conditions, and are adapted to the northernmost regions of rice cultivation, up to 53° N latitude. Genetic analysis revealed that the effects of PRR37 and Ghd7 alleles on heading date are additive, and PRR37 down-regulates Hd3a expression to suppress flowering under long-day conditions. Our results demonstrate that natural variations in PRR37/Hd2 and Ghd7/Hd4 have contributed to the expansion of rice cultivation to temperate and cooler regions

Modulating Strigolactone Signaling to Optimize Tomato Shoot Architecture for Vertical Farming

JiWoo Lee,Choon-Tak Kwon 한국육종학회 2023 한국육종학회 공동학술발표집 Vol.2023 No.-