The Role Of Wheat Flavonol Synthase Gene TaFLS2 In Drought Resistance And Development

Drought and other abiotic stresses reversely affect crop growth and production. Therefore, it appears to urgent to isolate resistant genes by research crop stress tolerance mechanisms with aim to achieve new stress-tolerant crop varieties. When suffered from environmental stimuli, plants will trigger complicated signaling network, which leads to comprehensive physiological alteration and finally produce adaptive response. Flavonoids are a kind of important secondary metabolites, and possess antioxidant and prooxidant activities to modulate redox homestiasis and alleviate oxidative damage. Flavonoids had six types, including flavonols and anthocyanins, of which flavonols exhibit the highest antioxidant and prooxidant activities. Flavonols are classified into six classes such as quercetin and kaempferol which differential antioxidant and prooxidant activities from each other. Different classes of flavonols had their own distribution patterns, and perform various functions. Flavonol synthase (FLS) catalyze the production of flavonol. Arabidopsis contains six copies FLS1～6, while the other flavonoid biosynthesis enzymes are single copy. Wheat, rice and other monocots, FLS and other flavonoid biosynthesis enzymes are multiple copies,Thus, the issue that whether different members of flavonol synthases (FLS) have catalysis specificities and participate in specific processes is not clear.Based on the previous transcriptomic anlaysis on the wheat introgression cultivar SR3 with high salt and drought tolerance and its parent wheat cultivar JN177, two wheat FLS genes, TαFLS1 and TαFLS2, were identified because of their drastical induction by drought. In the previous work, the drought resistance function and mechanism of TαFLS1 was in-depth studied,Found TαFLS1 mainly by promoting stomatal closure to increase drought resistance of plants, do not affect plant development; and TαFLS2 overexpression can not only improve drought resistance, also affected the process of plant development.This paper on the basis of the previous research, to analyzes the function of TαFLS2 in plant drought resistance and possible mechanism, and find it different from TαFLS1 in regulation of plant development.The results of the study for further research on FLS specificity family genes function and mechanism laid a foundation.1. The basis of droughttolerance by TaFLS2overexpressionIn comparison with Col-0, the seedlings of TaFLS2 overexpression (OE) lines had higher contents of flavonols, and their guard cells also accumulated more flavonols, indicating that TaFLS2 had in vivoactivity. Opposite to TaFLSl overexpresion lines that had lower anthocyanin content by shifting the homeostasis from anthocyanin branch to flavonol branch, TaFLS2 overexpression enhanced the activity of flavonoid and anthocyanin synthesis, indicating that flavonol accumulation by TaFLS2 overexpression feedback regulated the flavonoid synthesis pathway in a mannerdifferent from TaFLSl.We further studied the water-physiological basis of drought tolerance by TaFLS2 overexpression. Under osmotic stress stimulated by applying mannitol, the OE lines had superior growth ability and more lateral roots. Under the control and drought treatment, the OE lines had higher content of soluble sugar in comparison with Col-0. However, the water loss rate of detached leaves had no difference between Col-0 and TaFLS2 overexpressors. The results indicated that drought tolerance by TaFLS2 overexpression was associated with enhanced water absorption and maintenance capacity by accumulating more osmolytes. In comparison with Col-0, the OE lines had higher stomatal densities, and smaller stomatal aperture under drought, indicating that TaFLS2 overexpression affected both stomatal movement and development, and the opposite effect of these two alterations on transpiration efficiency led to no contribution to water loss rate. However, the previous results shown that alike TaFLS2, TaFLS1 overexpression promoted stomatal closure under drought, but opposite to TaFLS2, TaFLS1 overexpression promoted stomatal opening and had no effect on stomatal density.The previous results found that drought tolerance by TaFLS1 overexpression was also attributed to elevating ABA pathway as well as the activities of ROS producer and scavengers. Here, distinct from TaFLSl, TaFLS2 overexpression lines had comparable sensitivity to ABA and expression level of ABA synthesis and ABA-dependent signaling pathway associated genes, but the expression level of RD29A, a gene independent of ABA, was obviously increased. Similar to TaFLSl, TaFLS2overexpression lines had enhanced tolerance to exogenous H2O2, higher ROS level, stronger activities of ROS producer and scavengers and more transcript abundance of their encoding genes.2. The role of TaFLS2 in plant growth and developmentStudies have shown that flavonols can participate in plant development by inhibiting the auxin transport. In addition to increasing the number of stomata, We foundOE lines have leaf curl,saw blade and trichome number such auxin-related phenotypes. OE lines than wild-type seedlings large; NAA treatment, no significant changes in OE plants, wild type OE larger and similar strains,indicating that TaFLS2 over-expression caused flavonol-enriched affected of the auxin response.In summary, TaFLS2 overexpression enhanced drought tolerance via modulating water-physiology and redox homeostasis,on the other hand TaFLS2affect plant development by response to auxin In line with previous results, this work indicates that the difference in the function among FLS members, which is possibly associated with their catalysis specificity and feedback regulation of flavonoid synthesis and metabolism pathway. Notably, we can compare the association between crucial amino acid residues among FLS members and drought tolerance, and modify FLS genes to design FLS element offering stronger drought tolerance, which could be used for crop molecular breeding.