Submergence is a major constraint on rice production in South and Southeast Asia. In this study, we determined that a gene of the Sub1A-binding protein family, SAB23, encodes a plant homeodomain (PHD)-type transcription factor that has a novel function of negatively regulating submergence tolerance in rice. The T-DNA insertion mutant sab23 displayed reduced plant height, delayed seed maturation, and lower percentage seed set. Importantly, this mutant also exhibited enhanced submergence tolerance. In addition, CRISPR/Cas9 knock out of SAB23 resulted in a significant reduction in the content of the gibberellin GA4 and a dramatic increase in the content of GA1 in the plants. SAB23 binds to the promoter of CYTOCHROME P450 714B2 (CYP714B2), which encodes a GA13-oxidase that catalyses the conversion of GA53 to GA19. Disruption of SAB23 function led to increased CYP714B2 transcription, and overexpression of CYP714B2 produced phenotypes similar to those of the SAB23-knockout plants. Taken together, our results reveal that SAB23 negatively regulates rice submergence tolerance by modulating CYP714B2 expression, which has significant potential for use in future breeding.

Ipomoea nil (Linnaeus) Roth, belonging to the Convolvulaceae family, is an ornamental and medicinal plant in China, which has the function of diuretic and expectorant, and it is also a common weed in the field. In October 2021, a leaf spot disease was observed on I. nil in a field as weed in Jingzhou (N 30° 21', E 112° 19'), Hubei Province, China. Symptoms began as small brown blotches, then developed into oval or irregularly shaped brown necrotic lesions. In severe cases, the leaves were completely necrotic and detached. In the surveyed area, the incidence was between 30% - 40%. To isolate the pathogen, twenty-one leaf pieces (5×5 mm) were cut from the lesion edges of seven symptomatic leaves, disinfected with 70% ethanol and 2% sodium hypochlorite (NaOCl), rinsed with sterile water five times, then placed on three potato dextrose agar (PDA) modified with 50 μg/mL kanamycin, and incubated at 25 °C in dark for 5 days. The isolates were subcultured by transferring mycelium tips. Sixteen fungal strains were isolated from the tissues, and nine of them showed similar morphological characteristics. After cultured 7 days on PDA at 25 °C, the nine colonies were initially white, then turned greenish brown to black in the center and had abundant fine villous aerial mycelia up to 61.5 mm in average diameter. To examine its conidial morphology, the fungi were cultured for 7 days on potato carrot agar (PCA) at 22°C with a light/dark period of 8/16 h. On PCA, conidia were brown or olive-brown, obclavate to obpyriform, with a short beak, one to five transverse and zero to three longitudinal septa. They formed chains of 1 - 8 conidia, with branches. Conidia were 16 - 46 µm long and 8 - 14 µm wide (n=50). These morphological features were similar to those described in Alternaria spp. (Simmons 2007). A single isolate "Q2" was selected for molecular identification because it was the most aggressive in preliminary leaf pathogenicity assays. The internal transcribed spacer (ITS) region of rDNA and histone 3 (H3) gene were amplified and sequenced using primers ITS1/ITS4 (White et al. 1990) and H3-1a/H3-1b (Zheng et al. 2015). BLAST analysis revealed that the sequences (ITS, ON360984; H3, ON375577) were 100% identical to Alternaria alternata (ITS, MK396607; H3, MN840996), respectively. Maximum likelihood analysis based on combined two gene sequences was conducted with an evolutionary model of GTR+I+G under 1000 bootstrap replicates. Phylogenetic tree showed that Q2 and Alternaria alternata 21-5 and BLH-YB-11 located in one clade supported with 99% bootstrap values. The pathogen was identified as A. alternata. To fulfill Koch's postulate, 10 ml conidia (106 spores/ml) of Q2 was sprayed on five healthy seedlings, with sterile distilled water as a control. All leaves were rinsed three times with sterile water before inoculation. All seedlings were placed in sealed plastic bags with air valves, and grown in a greenhouse (25 ± 2 ˚C, RH 65%). The test was repeated twice. After 10 days, symptoms typical of brown blotches similar to those observed in the field were observed on leaves of inoculated plants, while control remained healthy. A. alternata was re-isolated from the inoculated symptomatic leaves with a frequency of 100% based on morphological and molecular characters, thus Koch's postulate was confirmed. To the best of our knowledge, this is the first report of A. alternata causing leaf spot on I. nil in China. Our findings extended the host range of the pathogen A. alternata on characteristic plants.

[目的]真菌内生细菌是一类特殊细菌,在寄主真菌体内及生态系统中发挥重要作用.前期从盘龙参菌根中筛选出一株含有内生细菌的真菌YZU172013(Phoma sp.),本研究进一步分离和鉴定YZU172013的内生细菌,并探索其生物学功能.[方法]首先通过16S rDNA序列扩增和SYTO-9染色检测YZU172013内生细菌的存在,接着用菌丝组织研磨法分离内生细菌,并通过形态及分子特征对其进行鉴定;然后运用特异引物验证细菌的内生性,并初步探究内生细菌的产胞外酶和耐药性等生物学功能;最后通过喂饲及注射初步探索了内生细菌的杀虫活性.[结果]真菌YZU172013能检测到细菌16S rDNA序列且菌丝内存在较多的细菌颗粒类似物.从YZU172013菌丝内分离出一株内生蜡样芽孢杆菌(Bacillus cereus 7-1Y),其营养体细胞仅为(1～1.5)μm×(0.3～0.5)μm,比普通蜡样芽孢杆菌小很多;通过蜡样芽孢杆菌特有的高丝氨酸环内酯酶(AHLase)序列扩增证明了其内生性.7-1Y具有水解淀粉、纤维素、解磷等功能.喂饲72 h后,家蚕代谢紊乱;注射24 h后家蚕的死亡率为100％.[结论]首次分离了一株真菌内生蜡样芽孢杆菌,该菌株7-1Y可产生多种胞外酶,且该细菌代谢物对昆虫血细胞具有较强毒性,具有很好的生防应用潜质.研究结果为真菌内生细菌的探究提供重要材料,为生防资源挖掘提供新思路.

Fusarium oxysporum KB-3 had been reported as a mycorrhizal fungus of Bletilla striata, which can promote the seed germination and vegetative growth. Endohyphal bacteria were demonstrated in the hyphae of the KB-3 by 16S rDNA PCR amplification and SYTO-9 fluorescent nucleic acid staining. A strain Klebsiella aerogenes KE-1 was isolated and identified based on the multilocus sequence analysis. The endohyphal bacterium was successfully removed from the wild strain KB-3 (KB-3−), and GFP-labeled KE-1 was also transferred to the cured strain KB-3− (KB-3+). The production of indole-3-acetic acid (IAA) in the culturing broths of strains of KE-1, KB-3, KB-3−, and KB-3+ was examined by HPLC. Their IAA productions were estimated using Salkowski colorimetric technique. The highest concentrations of IAA were 76.9 (at 48 h after inoculation), 31.4, 9.6, and 19.4 μg/ml (at 60 h after inoculation), respectively. Similarly, the three fungal cultural broths exhibited plant promoting abilities on the tomato root and stem growth. The results indicated that the ability of mycorrhizal Fusarium strain KB-3 to promote plant growth was enhanced because its endohyphal bacterium, Klebsiella aerogenes KE-1, produced a certain amount of IAA.

Waterlogging has increasingly become one of the major constraints to maize productivity in some maize production zones because it causes serious yield loss. Bulked segregant RNA-seq (BSR-seq) has been widely applied to profile candidate genes and map associated Single Nucleotide Polymorphism (SNP) markers in many species. In this study, 10 waterlogging sensitive and eight tolerant inbred lines were selected from 60 maize inbred lines with waterlogging response determined and preselected by the International Maize and Wheat Improvement Center (CIMMYT) from over 400 tropical maize inbred lines. BSR-seq was performed to identify differentially expressed genes and SNPs associated with waterlogging tolerance. Upon waterlogging stress, 354 and 1094 genes were differentially expressed in the tolerant and sensitive pools, respectively, compared to untreated controls. When tolerant and sensitive pools were compared, 593 genes were differentially expressed under untreated and 431 genes under waterlogged conditions, of which 122 genes overlapped. To validate the BSR-seq results, the expression levels of six genes were determined by qRT-PCR. The qRT-PCR results were consistent with BSR-seq results. Comparison of allelic polymorphism in mRNA sequences between tolerant and sensitive pools revealed 165 (normal condition) and 128 (waterlogged condition) high-probability SNPs. We found 18 overlapping SNPs with genomic positions mapped. Eighteen SNPs were contained in 18 genes, and eight and nine of 18 genes were responsive to waterlogging stress in tolerant and sensitive lines, respectively. Six alleles of the 18 originated from tolerant pool were significantly up-regulated under waterlogging, but not those from sensitive pool. Importantly, one allele (GRMZM2G055704) of the six genes was mapped between umc1619 and umc1948 on chromosome 1 where a QTL associated with waterlogging tolerance was identified in a previous research, strongly indicating that GRMZM2G055704 is a candidate gene responsive to waterlogging. Our research contributes to the knowledge of the molecular mechanism for waterlogging tolerance in maize.

Submergence is one of the major constraints to rice production in many rice growing areas in the world. The Sub1A gene has been demonstrated to dramatically improve submergence tolerance in rice. Here, we report the identification of a novel submergence response ( RS1 ) gene that is specifically induced in the Sub1A -mediated submergence tolerance response. Under submergence, RS1 was upregulated in M202 (Sub1A) but downregulated in M202 in RNA-seq and microarray assays. Expression analyses of various tissues and developmental stages show that RS1 mRNA levels are high in leaves and sheaths, but low in roots, stems, and panicles. Our results also show that RS1 is highly expressed under submergence, drought, and NaCl stresses, but not under cold or dehydration stress. Hormone ABA treatment induces, whereas GA treatment decreases, RS1 expression. The RS1 and Sub1A genes are co-regulated under submergence. Overexpression of RS1 in transgenic Kitaake (without Sub1A ) and M202( Sub1A )×Kitaake do not result in enhanced submergence tolerance. Conversely, down-regulation of RS1 in M202(Sub1A)×Kitaake lead to weaken submergence tolerance. We hypothesize that RS1 may play a role in the Sub1A -mediated submergence tolerance pathway. Key word: Rice ( Oryza sativa L.), submergence, RNA-seq, Sub1A , abiotic stress.