Expression of AtNF-YB1 activates early flowering, showing potential in breeding hybrid rice.

The nuclear factor Y (NF-Y) has been shown to be involved in plant growth and development in response to various environmental signals. However, the integration of these mechanisms into breeding practices for new cultivars has not been extensively investigated. In this study, the Arabidopsis gene AtNF-YB1 was introduced into rice, including inbred Kasalath and the hybrids Jinfeng × Chenghui 727 and Jinfeng × Chuanhui 907. The obtained transgenic rice showed early flowering under both natural long day (NLD) and natural short day (NSD) conditions. For the inbred Kasalath, the transgenic lines clearly showed a shorter plant height and lower grain yield, with a decrease in spike length and grain number but more productive panicles. However, the hybrids with AtNF-YB1 had much smaller or even zero reduction in spike length and grain number and more productive panicles. Thus, maintained or even increased grain yields of the transgenic hybrids were recorded under the NLD conditions. Quantitative PCR analysis indicated that the rice flowering initiation pathways were early activated via the suppression of Ghd7 induction in the transgenic rice. RNA-Seq further demonstrated that three pathways related to plant photosynthesis were markedly upregulated in both Jinfeng B and the hybrid Jinfeng × Chuanhui 907 with AtNF-YB1 expression. Moreover, physiological experiments showed an upregulation of photosynthetic rates in the transgenic lines. Taken together, this study suggests that AtNF-YB1 expression in rice not only induces early flowering but also benefits photosynthesis, which might be used to develop hybrid varieties with early ripening.

Overexpression of OsNF-YB4 leads to flowering early, improving photosynthesis and better grain yield in hybrid rice.

For cereal crops, such as rice, the grain yield mainly comes from the accumulation of carbohydrates in the seed, which depends ultimately on photosynthesis during the growth period. To create early ripen variety, higher efficiency of photosynthesis is thus necessary to get higher grain yield with shorter growth period. In this study, flowering early was observed in the hybrid rice with overexpression of OsNF-YB4. Along with the flowering early, the hybrid rice also was shorter in plant height with less of leaves and internodes, but no changes of panicle length and leaf emergence. The grain yield was kept or even increased in the hybrid rice with shorter growth period. Transcription analysis revealed that Ghd7-Ehd1-Hd3a/RFT1 was activated early to promote the flowering transition in the overexpression hybrids. RNA-Seq study further showed that carbohydrate-related pathways were significantly altered in addition to circadian pathway. Notably, up-regulation of three pathways related to plant photosynthesis was observed, as well. Increased carbon assimilation with alteration of chlorophyll contents was subsequently detected in the following physiological experiments. All these results demonstrate that overexpression of OsNF-YB4 in the hybrid rice activates flowering early and improves photosynthesis resulting in better grain yield with shorter growth period.

Genomic Characterization of a Tomato Yellow Mottle-Associated Virus Collected from a Field Tomato Plant in Chengdu, Southwestern China.

Here, we report the genomic sequence and genetic variations of a Tomato yellow mottle-associated virus. The virus isolated from a field tomato (Solanum lycopersicum) plant in Chengdu, southwestern China, was sequenced via both Illumina and Sanger technologies. Phylogeny indicates that its genome is close to the reported virus sequence from S. lycopersicum collected in 2013 but far from Solanum nigrum collected in 2020.

Characterization and Evaluation of Transgenic Rice Pyramided with the Pi Genes Pib, Pi25 and Pi54.

BACKGROUND: Emergence of new pathogen strains of Magnaporthe oryzae is a major reason for recurrent failure of the resistance mediated by a single resistance gene (Pi) in rice. Stacking various Pi genes in the genome through marker-assisted selection is thus an effective strategy in rice breeding for achieving durable resistance against the pathogen. However, the effect of pyramiding of multiple Pi genes using transgenesis still remains largely unknown. RESULTS: Three Pi genes Pib, Pi25 and Pi54 were transferred together into two rice varieties, the indica variety Kasalath and the japonica variety Zhenghan 10. Transgenic plants of both Kasalath and Zhenghan 10 expressing the Pi transgenes showed imparted pathogen resistance. All the transgenic lines of both cultivars also exhibited shorter growth periods with flowering 2-4 days early, and shorter plant heights with smaller panicle. Thus, pyramiding of the Pi genes resulted in reduced grain yields in both rice cultivars. However, tiller numbers and grain weight were generally similar between the pyramided lines and corresponding parents. A global analysis of gene expression by RNA-Seq suggested that both enhancement and, to a lesser extent, inhibition of gene transcription occurred in the pyramided plants. A total of 264 and 544 differentially expressed genes (DEGs) were identified in Kasalath and Zhenghan 10, respectively. Analysis of the DEGs suggested that presence of the Pi transgenes did not alter gene expression only related to disease resistance, but also impacted many gene transcriptions in the pathways for plant growth and development, in which several were common for both Kasalath and Zhenghan 10. CONCLUSION: Pyramiding of the Pi genes Pib, Pi25 and Pi54 via transgenesis is a potentially promising approach for improving rice resistance to the pathogen Magnaporthe oryzae. However, pleiotropic effects of the Pi genes could potentially result in yield loss. These findings support the idea that immunity is often associated with yield penalties. Rational combination of the Pi genes based on the genetic background may be important to balance yield and disease resistance.

Nuclear factor OsNF-YB4 promotes flowering by negatively regulating the floral repressor gene Ghd7 in rice.

Flowering time or heading date is a critical agronomic trait of rice and is regulated by numerous genes, including several genes encoding nuclear factor YB (NF-YB) in rice, NF-YB11 is one of the genes well known to be involved in the process, delaying flowering under long-day (LD) conditions but promoting flowering under short-day (SD) conditions. In this study, we identified another NF-YB gene, OsNF-YB4. Overexpression of OsNF-YB4 promoted rice flowering under both natural long-day (NLD) and natural short-day (NSD) conditions, whereas suppression or loss-of-function of this gene delayed flowering. The transcription of OsNF-YB4 exhibited an obvious circadian pattern and was induced by light under both LD and SD conditions. Expression analyses of flowering regulators in the photoperiodic flowering pathway demonstrated that up-regulation of OsNF-YB4 resulted in down-regulation of floral repressor Grain number, plant height and heading date 7 (Ghd7), and thus activating the Early heading date 1 (Ehd1)-mediated flowering pathway. Besides, OsNF-YB4 was observed to bind to the specific CCAAT-box regions in the Ghd7 promoter in vitro and interact with GHD7 in yeast. All these evidences support that OsNF-YB4 functions as a flowering promoter by negatively regulating the expression of floral repressor Ghd7 in rice photoperiodic flowering-time regulatory network.

The AC4 Protein of a Cassava Geminivirus Is Required for Virus Infection.

Geminiviruses (family Geminiviridae) are among the most devastating plant viruses worldwide, causing severe damage in crops of economic and subsistence importance. These viruses have very compact genomes and many of the encoded proteins are multifunctional. Here, we investigated the role of the East African cassava mosaic Cameroon virus (EACMCV) AC4 on virus infectivity in Nicotiana benthamiana. Results showed that plants inoculated with EACMCV containing a knockout mutation in an AC4 open reading frame displayed symptoms 2 to 3 days later than plants inoculated with wild-type virus, and these plants recovered from infection, whereas plants inoculated with the wild-type virus did not. Curiously, when an additional mutation was made in the knockout mutant, the resulting double mutant virus completely failed to cause any apparent symptoms. Interestingly, the role of AC4 on virus infectivity appeared to be dependent on an encoded N-myristoylation motif that mediates cell membrane binding. We previously showed that EACMCV containing the AC4T38I mutant produced virus progeny characterized by second-site mutations and reversion to wild-type virus. These results were confirmed in this study using additional mutations. Together, these results show involvement of EACMCV AC4 in virus infectivity; they also suggest a role for the combined action of mutation and selection, under prevailing environmental conditions, on begomovirus genetic variation and diversity.

Genetic variability of East African cassava mosaic Cameroon virus under field and controlled environment conditions.

Cassava geminiviruses occur in all cassava growing areas of Africa and are considered to be the most damaging vector-borne plant pathogens. At least seven species of these viruses have been identified. We investigated genetic variation in East African cassava mosaic cassava Cameroon virus (EACMCV) from naturally infected cassava and from experimentally infected Nicotiana benthamiana. Results showed that the populations of EACMCV in cassava and in N. benthamiana were genetically heterogeneous. Mutation frequencies in the order of 10(-4), comparable to that reported for plant RNA viruses, were observed in both hosts. We also produced an EACMCV mutant that induces reversion and second site mutations, thus suggesting that a high mutation frequency facilitates the maintenance of genome structure and function. This is direct experimental evidence showing that cassava geminiviruses exhibit a high mutation frequency and that a single clone quickly transforms into a collection of mutant sequences upon introduction into the host.

Spatial distribution of transcript changes in the maize primary root elongation zone at low water potential.

BACKGROUND: Previous work showed that the maize primary root adapts to low Psiw (-1.6 MPa) by maintaining longitudinal expansion in the apical 3 mm (region 1), whereas in the adjacent 4 mm (region 2) longitudinal expansion reaches a maximum in well-watered roots but is progressively inhibited at low Psiw. To identify mechanisms that determine these responses to low Psiw, transcript expression was profiled in these regions of water-stressed and well-watered roots. In addition, comparison between region 2 of water-stressed roots and the zone of growth deceleration in well-watered roots (region 3) distinguished stress-responsive genes in region 2 from those involved in cell maturation. RESULTS: Responses of gene expression to water stress in regions 1 and 2 were largely distinct. The largest functional categories of differentially expressed transcripts were reactive oxygen species and carbon metabolism in region 1, and membrane transport in region 2. Transcripts controlling sucrose hydrolysis distinguished well-watered and water-stressed states (invertase vs. sucrose synthase), and changes in expression of transcripts for starch synthesis indicated further alteration in carbon metabolism under water deficit. A role for inositols in the stress response was suggested, as was control of proline metabolism. Increased expression of transcripts for wall-loosening proteins in region 1, and for elements of ABA and ethylene signaling were also indicated in the response to water deficit. CONCLUSION: The analysis indicates that fundamentally different signaling and metabolic response mechanisms are involved in the response to water stress in different regions of the maize primary root elongation zone.

Activation of hypersensitive cell death by pathogen-induced receptor-like protein kinases from Arabidopsis.

In Arabidopsis, there is a family of receptor-like protein kinases (RLKs) containing novel cysteine-rich repeats in their extracellular domains. Genes encoding many of these cysteine-rich RLKs (CRKs) are induced by pathogen infection, suggesting a possible role in plant defense responses. We have previously generated Arabidopsis plants expressing four pathogen-regulated CRK genes (CRK5, 6, 10 and 11) under control of a steroid-inducible promoter and found that induced expression of CRK5, but not the other three CRK genes, triggered hypersensitive response-like cell death in transgenic plants. In the present study, we have analyzed the structural relationship of the CRK family and identified three CRKs (CRK4, 19 and 20) that are structurally closely related to CRK5. Genes encoding these three CRKs are all induced by salicylic acid and pathogen infection. Furthermore, induced expression of CRK4, 19 and 20 all activates rapid cell death in transgenic plants. Thus, the activity of inducing rapid cell death is shared by these structurally closely related CRKs. We have also performed yeast two-hybrid screens and identified proteins that interact with the kinase domains of CRKs. One of the identified CRK-interacting proteins is the kinase-associated type 2C protein phospohatase known to interact with a number of other RLKs through its kinase-interacting FHA domain. Other CRK-interacting proteins include a second protein with a FHA domain and another type 2C protein phosphatase. Interactions of CRKs with these three proteins in vivo were demonstrated through co-immunoprecipitation. These CRK-interacting proteins may play roles in the regulation and signaling of CRKs.

Sensitization of defense responses and activation of programmed cell death by a pathogen-induced receptor-like protein kinase in Arabidopsis.

During the search for potential target genes of WRKY DNA-binding transcription factors, we have previously identified four pathogen-induced Arabidopsis genes (CRK5, CRK6, CRK10 and CRK11) encoding receptor-like protein kinases (RLKs) containing novel cysteine-rich repeats in their extracellular domains. In the present study, we transformed Arabidopsis plants with the RLK genes under control of the constitutive CaMV 35S promoter or a steroid-inducible Ga14 promoter. Expression of CRK5, but not the three other RLK genes, resulted in significant alterations in defense responses and leaf growth in transgenic plants. In transgenic plants harboring the 35S::CRK5 construct, significantly elevated and constitutive expression of CRK5 correlated with enhanced leaf growth and increased resistance to the bacterial pathogen Pseudomonas syringae. The enhanced disease resistance in the transgenic plants was associated with more rapidly induced expression of the PR1 gene after pathogen infection. In transgenic plants transformed with CRK5 under control of the steroid-inducible promoter, expression of the transgene was induced at relatively high levels after the steroid application and this induced expression of CRK5 triggered hypersensitive response-like cell death. Induced CRK5 expression also activated cell death in the npr1, ndr1 and eds1 mutants and in the transgenic nahG plants that fail to accumulate salicylic acid. Thus, the novel RLK is capable of activating multiple distinct defense responses depending on the manner and/or the levels of its over-expression in transgenic plants.