Integrated transcriptome and metabolite profiling highlights the role of benzoxazinoids in wheat resistance against Fusarium crown rot

Fusarium crown rot(FCR), caused by Fusarium spp., is a chronic and severe plant disease worldwide. In the last years, the incidence and severity of FCR in China has increased to the point that it is now considered a threat to local wheat crops. In this study, for the first time, the metabolites and transcripts responsive to FCR infection in the partial resistant wheat cultivar 04 Zhong 36(04 z36) and susceptible cultivar Xinmai 26(XM) were investigated and compared at 20 and 25 days post inoculation(dpi). A total of 443 metabolites were detected, of which 102 were significantly changed because of pathogen colonization.Most of these 102 metabolites belonged to the flavonoid, phenolic acid, amino acid and derivative classes.Some metabolites, such as proline betaine, lauric acid, ribitol, and arabitol, were stably induced by Fusarium pseudograminearum(Fp) infection at two time points and may have important roles in FCR resistance. In line with the reduced seedling height of 04 z36 and XM plants, RNA-seq analysis revealed that FCR infection significantly affected the photosynthesis activities in two cultivars. Furthermore, 15 jasmonate ZIM-domain genes(JAZ) in the significantly enriched ‘regulation of jasmonic acid mediated signaling pathway’ in 04 z36 were down-regulated. The down-regulation of these JAZ genes in 04 z36 may cause a strong activation of the jasmonate signaling pathway. Based on combined data from gene expression and metabolite profiles, two metabolites, benzoxazolin-2-one(BOA) and 6-methoxy-benzoxazolin-2-one(MBOA), involved in the benzoxazinoid-biosynthesis pathway, were tested for their effects on FCR resistance. Both BOA and MBOA significantly reduced fungal growth in vitro and in vivo, and, thus, a higher content of BOA and MBOA in 04 z36 may contribute to FCR resistance. Above all, the current analysis extends our understanding of the molecular mechanisms of FCR resistance/susceptibility in wheat and will benefit further efforts for the genetic improvement of disease resistance.

Expression and regulation of genes involved in the reserve starch biosynthesis pathway in hexaploid wheat (Triticum aestivum L.)

Reserve starch of cereal crop accounts for about 70%of grain endosperm and acts as an important human carbohydrate resource worldwide.Wheat reserve starch is synthesized by enzymatic machinery in endosperm cells.To identify genes involved in starch biosynthesis,we constructed 30 RNA-Seq libraries of 10 endosperm-development periods and performed expression and localization analyses.Of 166 endosperm-expressed homologs of starch biosynthesis-related genes,74 showed expression correlated with reserve starch accumulation,including 26 with expected subcellular distribution and higher expression than their isoforms.The key proteins SUS3,UGP1,cAGPase,and Bt1-3 formed the main metabolic pathway and contributed the major substrates for starch processing in amyloplasts.Important isoforms,key pathway proteins,and the main carbon flux toward starch formation in the reserve starch biosynthesis pathway were identified.Based on a coexpression analysis,a library of 425 transcription factors was produced to screen for common regulators.TaMYB44 had features of transcription factors and bound to TaSUT1,TaSSIIIa,TaBEIIa,TaISA1,and TaBEIIb promoters in yeast,suggesting that the gene is a pathway regulator.This study sheds light on understanding the mechanism of reserve starch biosynthesis and will be helpful for increasing starch content in wheat endosperm via biotechnological strategies.