Summary Grain length is one of the most important factors in determining wheat yield. Here, a stable QTL for grain length was mapped on chromosome 1B in a F10 recombinant inbred lines (RIL) population, and the gene TaGL1‐B1 encoding carotenoid isomerase was identified in a secondary large population through multiple strategies. The genome‐wide association study (GWAS) in 243 wheat accessions revealed that the marker for TaGL1‐B1 was the most significant among all chromosomes. EMS mutants of TaGL1 possessed significantly reduced grain length, whereas TaGL1‐B1‐overexpressed lines possessed significantly increased grain length. Moreover, TaGL1‐B1 strongly interacted with TaPAP6. TaPAP6‐overexpressed lines had significantly increased grain length. Transcriptome analysis suggested that TaPAP6 was possibly involved in the accumulation of JA (jasmonic acid). Consistently, JA content was significantly increased in the TaGL1‐B1 and TaPAP6 overexpression lines. Additionally, the role of TaGL1‐B1 in regulating carotenoids was verified through QTL mapping, GWAS, EMS mutants and overexpression lines. Notably, overexpression of TaGL1‐B1 significantly increased wheat yield in multiple locations. Taken together, overexpression of TaGL1‐B1 enhanced grain length, probably through interaction with TaPAP6 to cause the accumulation of JA that improved carotenoid content and photosynthesis, thereby resulted in increased wheat yield. This study provided valuable genes controlling grain length to improve yield and a potential insight into the molecular mechanism of modulating JA‐mediated grain size in wheat.
Tussilago farfara is widely distributed in China, India, Iran, Pakistan, Russia, Western Europe and North Africa. The flower bud of T. farfara has medicinal value used for the treatment of cough, asthma, phlegm and angiocardiopathy (Chen 1999). During the rainy season of July 2019, many small spots were observed on 70% of the leaves of Tussilago farfara plants in Hezheng Medicinal Botanical Garden. The botanical garden is affiliated with Gansu University of Chinese Medicine and located in Hezheng county, Linxia Hui Autonomous Prefecture, Gansu, China. Eventually, the center of the lesion turned into light brown as symptoms progressed. Diseased tissues were cut into small pieces and put onto moist filter papers within Petri-dishes further incubated at 25°C (humidity around 90%). After one day, Alternaria spores developed from the edge of necrotic tissues. Spores were singly picked up and transferred to potato dextrose agar (PDA). Pure cultures were deposited in the Fungi Herbarium of Yangtze University (YZU), Jingzhou, Hubei, China. All strains were similar to each other and two (YZU 191293 and YZU 191294) were selected for further studies. Three to four-day old mycelial plugs (6 mm in diameter) were transferred onto fresh PDA plates (90 mm in diameter) incubated at 25 °C in dark. After 7 days, colonies were 65 to 67 mm in diameter, hazel to buff from the center to edge, reverse side fuscous black to creamy white. The isolated fungus was cultured on V8 juice agar (V8A) at 22°C under an 8h photoperiod for 7 days for microscopic observations (Simmons 2007). Conidiophores were straight or curved, 30 to 90 µm long, 4 to 7 µm wide. Conidia were solitary or 2 to 3 in a chain, long ellipsoid to obclavate, 1 to 8 transverse septa, 40 to 125 µm long, 8 to 36 µm wide; blunt-tapered beak variable in length 14 to 32 µm long, 6 to 10 µm wide. Morphologically, the fungus was identified as Alternaria cinerariae according to previous descriptions (Simmons 2007, Nishikawa and Nakashima 2015). Genomic DNA was extracted from 3-day-old mycelium grown on PDA (Cenis 1992). Three gene regions including rDNA ITS (ITS4/ITS5), RPB2 (RPB2-5F/RPB2-7cR), EF-1α (EF1-728F/EF1-986R) were amplified and sequenced according to Woudenberg et al. (2013). The resulted sequences were 100% similar to those of the representative strain CBS 116495 (GenBank acc. nos. KC584190 of ITS, KC584389 of RPB2, and KC584648 of EF-1α, respectively) of Alternaria cinerariae in GenBank database during BLAST searches. Maximum likelihood analysis was performed using the combined dataset of the three gene regions after alignment under 1000 bootstrap replicates with the model of SYM+I+G. Phylogenetic tree showed that the present strains and A. cinerariae CBS 116495 fell into a clade with 100% bootstrap value support. Based on morphological characteristics and phylogenetic analysis, the isolated fungus was identified as A. cinerariae. To confirm its pathogenicity, 20 µL conidial suspension (3×105 spores/mL) was dropped on living leaves (n=3) of Tussilago farfara plants (n=3) which were cultivated for one month after transplantation as seedlings. Controls were treated with sterile distilled water. The plants were cultivated in greenhouse under supplemental fluorescent light at 25°C and covered by plastic bags to maintain humidity around 90%. The experiment was repeated three times. After 2 days, brown spots, 6 to 8 mm in size, were observed on the inoculated leaves. Gradually, the lesions enlarged to the leaf edge and leaves became blighted and shrunken. All control plants were symptomless. The same fungus was re-isolated from the lesions of symptomatic plants and identified using the EF-1α gene sequence. To our knowledge, this is the first report of A. cinerariae causing leaf spot on Tussilago farfara.
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