Hong-Hui Lin’s research while affiliated with Sichuan University and other places

The spindle assembly checkpoint (SAC) ensures faithful chromosome segregation during cell division by monitoring kinetochore-microtubule attachment. Plants produce both sequence-conserved and diverged SAC components, and it has been largely unknown how SAC activation leads to the assembly of these proteins at unattached kinetochores to prevent cells from entering anaphase. In Arabidopsis thaliana , the noncanonical BUB3.3 protein was detected at kinetochores throughout mitosis, unlike MAD1 and the plant-specific BUB1/MAD3 family protein BMF3 that associated with unattached chromosomes only. When BUB3.3 was lost by a genetic mutation, mitotic cells often entered anaphase with misaligned chromosomes and presented lagging chromosomes after they were challenged by low doses of the microtubule depolymerizing agent oryzalin, resulting in the formation of micronuclei. Surprisingly, BUB3.3 was not required for the kinetochore localization of other SAC proteins or vice versa. Instead, BUB3.3 specifically bound to BMF3 through two internal repeat motifs that were not required for BMF3 kinetochore localization. This interaction enabled BMF3 to recruit CDC20, a downstream SAC target, to unattached kinetochores. Taken together, our findings demonstrate that plant SAC utilizes unconventional protein interactions for arresting mitosis, with BUB3.3 directing BMF3’s role in CDC20 recruitment, rather than the recruitment of BUB1/MAD3 proteins observed in fungi and animals. This distinct mechanism highlights how plants adapted divergent versions of conserved cell cycle machinery to achieve specialized SAC control.

Phosphate (Pi) is essential for plant growth and development. One strategy to improve Pi use efficiency is to enhance Pi remobilization among leaves. Using transcriptome analysis with first (top) and fourth (down) leaf blades from rice ( Oryza sativa ) in Pi‐sufficient and deficient conditions, we identified 1384 genes differentially expressed among these leaf blades. These genes were involved in physiological processes, metabolism, transport, and photosynthesis. Moreover, we identified the Pi efflux transporter gene, OsPHO1;3 , responding to Pi‐supplied conditions among these leaf blades. OsPHO1;3 is highly expressed in companion cells of phloem, but not xylem, in leaf blades and induced by Pi starvation. Mutation of OsPHO1;3 led to Pi accumulation in second to fourth leaves under Pi‐sufficient conditions, but enhanced Pi levels in first leaves under Pi‐deficient conditions. These Pi accumulations in leaves of Ospho1;3 mutants resulted from induction of OsPHT1;2 and OsPHT1;8 in root and reduction of Pi remobilization in leaf blades, revealed by the decreased Pi in phloem of leaves. Importantly, lack of OsPHO1;3 caused growth defects under a range of Pi‐supplied conditions. These results demonstrate that Pi remobilization is essential for Pi homeostasis and plant growth irrespective of Pi‐supplied conditions, and OsPHO1;3 plays an essential role in Pi remobilization for normal plant growth.

Phosphorus is one of the macro-elements required by plants, but phosphate (Pi), the only form that can be absorbed by plants, is always limited for plant growth and development. To adapt to Pi deficiency, plants have evolved a complex regulatory system to improve Pi acquisition and utilization efficiency. In this study, metabolomic and transcriptomic analyses were performed to exam the global metabolites and gene expressions profiles responding to Pi deficiency in rice. A total of 23 metabolites were co-changed in leaves and roots after Pi deficiency, with sucrose, trehalose and melibiose significant accumulated. A total of 779 genes were co-changed in these leaves and roots. Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that differentially expressed genes and differentially accumulated metabolites were co-enriched in galactose metabolism. Further exogenous sugars supply with rice roots could induce Pi starvation responsiveness and the expression of OsPHR2, which codes the central regulator for Pi starvation responsiveness in rice. This work revealed the interaction between sugars and phosphate in rice, and the importance of OsPHR2 in this interaction.

Given the important roles that seed‐borne endophytes can play on their plant hosts, comprehensive studies of the bacterial and fungal communities of seeds are of great importance. In this study, we assessed the seed endophytes of three gramineous (Avena sativa, Elymus sibiricus and Elymus dahuricus) and four leguminous (Vicia villosa, Trifolium repens, Trifolium pretense and Medicago sativa) forages using high‐throughput sequencing. In total, 1013 distinct bacterial operational taxonomic units (OTUs) and 922 fungal OTUs were detected, with bacteria and fungi per sample ranging from 240 to 425 and 261 to 463 respectively. These seven forages shared a high number of potentially beneficial taxa, including Bacillus, Pantoea, Candida and Helotiales, but the relative proportion of these taxa was different in each seed. Fungal communities were clustered more distinctively by host genotypes than bacterial. Some bacterial taxa may be involved in the recruitment of genera from the same phylum. Three Pantoea sp. and five Bacillus sp. were isolated from seeds, and all showed positive effects on Medicago sativa germination rate under salt stress, and of these, Bacillus subtilis Es‐1 and Pantoea agglomerans Ed‐3 performed best, but their influence was affected by the seed’s microbiome. Rather than simply promoting host plant growth directly, some taxa may also participate in organizing the assembly of plant microbiomes which will influence seed response to biological factors. This study uses a new, high‐throughput sequencing based strategy to identify beneficial strains and analyse the interactions between microorganisms and plants to maximize microbial functions in long‐term agricultural practices.

Elymus, the largest genus of the Triticeae Dumort, is a forage grass in the Qinghai-Tibetan Plateau, where the climate has gradually become increasingly dry in recent years. To understand the mechanisms of the response to drought stress in Elymus species, we first investigated physiological and biochemical responses to polyethylene glycol (PEG-6000) simulated drought stress in two Elymus species, Elymus nutans and Elymus sibiricus, and found that E. nutans was more tolerant to drought stress than E. sibiricus. De novo transcriptome analysis of these two Elymus species treated with or without 10% PEG-6000 revealed that a total of 1695 unigenes were commonly regulated by drought treatment in these two Elymus species, with 1614 unigenes up-regulated and 81 unigenes down-regulated. The coexpressed differentially expressed genes (DEGs) were enriched in regulation of transcription and gene expression in the GO database. KEGG pathway analysis indicated plant hormone signaling transduction were mostly enriched in co-expressed DEGs. Furthermore, genes annotated in the plant hormone signaling transduction were screened from co-expressed DEGs, and found that abscisic acid plays the major role in the drought stress tolerance of Elymus. Meanwhile, transcription factors screened from co-expressed DEGs were mainly classified into the ERF subfamily and WRKY, DREB, and HSF family members. Our results provide further reference for studying the response mechanism and culturing highly tolerant grasses of the Elymus species under drought stress.

Background: The grasses in adverse environment such as Qinghai-Tibet Plateau are hypothesized to survive the harsh climate in part upon their seed-borne microorganisms, and yet the characteristics of the grass seed microbial communities remain undetermined. Here, we assessed the seed microbial communities of three native gramineous grass species (Avena sativa, Elymus sibiricus and Elymus dahuricus) and four candidate legumes (Vicia villosa, Trifolium repens, Trifolium pretense and Medicago sativa) on the Qinghai-Tibet Plateau by high-throughput sequencing. Results: A total of 1,013 bacterial operational taxonomic units (OTUs) and 922 fungal OTUs were observed. The OTUs that shared in all the samples were in high abundance but with different relative abundances. The majority of bacterial sequences were assigned to Proteobacteria (54~90%) and Firmicutes (5~41%), and the fungal communities were mainly composed of Ascomycota (23~96%) and Basidiomycota (2~11%). The fungal communities were more affected by host genetic distance than bacteria. The three gramineous grasses were speculated to survive the adversity partly due to their high abundance of beneficial bacteria like Pantoea or Bacillus, and non-pathogenic fungi like Candida or unclassified Helotiaceae. Also enriched with these potential beneficial taxa, the four leguminous grasses may be competent to adapt the Qinghai-Tibet Plateau stress. Furthermore, the higher tolerance grasses (Elymus sibiricus and Elymus dahuricus) possessed a greater number of growth-promoting and tolerance bacterial and non-pathogenic fungi. Conversely, the less tolerance grass Medicago sativa contained lower levels of such microorganisms, and showed higher abundance of pathogenic taxa. Furthermore, the isolated Bacillus subtilis or Pantoea agglomerans could more probably promote seeding growth of hosts with lower abundance of them, while inhibit if the endo-abundance of was high. Conclusions: Seed-resident microbiome structure of the four cold-tolerance legumes and three Qinghai-Tibet Plateau gramineae is host dependent and related to stress resistance. It also has a strong influence on the response of seedlings to biological seed treatments. This study provides valuable data for studying plant resilience, identifying more biocontrol strains, maximizing microbial functions in ‘smart farming’ practices.

Phosphorus (P) is an essential macronutrient required for plant development and production. The mechanisms regulating phosphate (Pi) uptake are well established, but the function of chloroplast Pi homeostasis are poorly understood in rice. PHT2;1 is one of the transporters/translocators mediating Pi import into chloroplasts. In this study, to gain insight into the role of OsPHT2;1‐mediated stroma Pi, we analyzed OsPHT2;1 function in Pi utilization and photoprotection. Our results showed that OsPHT2;1 was induced by Pi starvation and light exposure. Cell‐based assays showed that OsPHT2;1 localized to the chloroplast envelope and functioned as a low‐affinity Pi transporter. The ospht2;1 had reduced Pi accumulation, plant growth and photosynthetic rates. Metabolite profiling revealed that 52.6% of the decreased metabolites in ospht2;1 plants were flavonoids, which was further confirmed by 40% lower content of total flavonoids compared to wild type. As a consequence, ospht2;1 plants were more sensitive to UV‐B irradiation. Moreover, the content of phenylalanine, the precursor of flavonoids, was also reduced, and largely associated with the repressed expression of ADT1/MTR1. Furthermore, the ospht2;1 showed decreased grain yields at relatively high levels of UV‐B irradiance. In summary, OsPHT2;1 functions as a chloroplast‐localized low‐affinity Pi transporter that mediates UV tolerance and rice yields in different latitudes.

Phosphorus is one of the most important macronutrients required for plant growth and development. The importance of phosphorylation modification in regulating phosphate (Pi) homeostasis in plants is emerging. We performed phosphoproteomic profiling to characterize proteins whose degree of phosphorylation is altered in response to Pi starvation in rice root. A subset of 554 proteins, including 546 down-phosphorylated and eight up-phosphorylated proteins, exhibited differential phosphorylation in response to Pi starvation. KEGG pathway analysis with the differentially phosphorylated proteins indicated that RNA processing, transport, splicing and translation and carbon metabolism played critical roles in response to Pi starvation in rice. Levels of phosphorylation of four mitogen-activated protein kinases (MAPKs) including OsMAPK6, five calcium-dependent protein kinases (CDPKs) and OsCK2β3 decreased in response to Pi starvation. The decreased phosphorylation level of OsMAPK6 was confirmed by western blotting. Mutation of OsMAPK6 led to Pi accumulation under Pi-sufficient conditions. Motif analysis indicated that the putative MAPK, CK2 and CDPK substrates represented about 54.4%, 21.5% and 4.7%, respectively, of the proteins exhibiting differential phosphorylation. Based on the motif analysis, 191, 151 and 46 candidate substrates for MAPK, CK2 and CDPK were identified. These results indicate that modification of phosphorylation profiles provides complementary information on Pi-starvation-induced processes, with CK2, MAPK and CDPK protein kinase families playing key roles in these processes in rice.

Global warming is considered a pivotal environmental factor influencing the growth of meadow forage grasses and the balance of alpine meadow ecosystems, especially on the Qinghai–Tibet Plateau. The objective of this study was to evaluate the adaptability of introducing and restoring forage grass species on the Hongyuan prairie in response to temperature changes. Based on the analysis of photosynthetic parameters such as PN, GS, CI, Vcmax, Jmax, Fv/Fm, Fv′/Fm′, qP, and ΦPSII for different forage grass species grown in the alpine meadow area, we found the local native grass species had photosynthetic capacities that were more sensitive to temperature changes than those of the introduced species. Among the several kinds of introduced forage grasses, reed canary grass showed the greatest redistribution of absorbed light energy when light energy exceeded the utilization capacity. Reed canary grass also showed an increased distribution of biomass in its roots and a decreased distribution of biomass in its stems. Overall, reed canary grass is a potential resource to address grassland desertification and to restore or reconstruct meadow grass ecosystems in accordance with the temperature changes.