Multi-regression And Path Analysis For Growth-related Quantitative Traits And Relationship Between Gene Expression Of UDP-glucose Pyrophosphorylase And Agar Yield In Gracilariopsis Lemaneiformis(Rhodophyta)

(?)Gracilariopsis lemaneiformis is a cultivated algae species with economic importance.In this study,5 growth-related quantitative traits were measured,including fresh weigh(FW),first branch length(FBL),stem diameter(SD),number of second branches(SBN),and total length of second branches(SBL).Multiple linear-regression analysis and path analysis were done among these quantitative traits to evaluate their relation and their contribution to the biomass(FW)output.Among these traits,SBL showed the highest CV value,suggesting total length of second branches as the most important influence factor in the breeding of this algae.Correlation analysis indicated that FW had significantly positive correlations(P<0.01)with other 4 traits.Correlation analysis and path analysis confirmed that total length of second branches influenced fresh weigh the most(Pearson linear-correlation coefficient=0.639,path coefficient=0.650),and selecting new stains with long total length of second branches as cultivar in the industrialization of G.lemaneiformis would help to increase the yield.Using data from model group,we also constructed reliable multiple linear-regression equation with FW as dependent variable:YFW=-1.511+0.6 13XFBL+1.395XSD-0.615XSBN+0.651 XSBL(R2=0.753),and paired T-test with data of verification group suggested this model could be applied to select possible strains with better growth potential in the progress of breeding and cultivation of G.lemaneiformis.(?)UDP-glucose pyrophosphorylase(UGPase)is an enzyme involved in the biosynthesis of UDP-D-galactose,a subunit of agar in red seaweeds.The relationship between agar content and expression levels of the UGPase encoding gene(glugp)was studied in thalli under different treatment conditions using a quantitative real-time PCR-based method(qPCR).Moreover,this qPCR method for the measurement of glugp expression was also applied to commercial varieties of G.lemaneiformis,a red macroalgae,in order to examine its reliability on material obtained from field cultivation.Both the agar content and glugp gene expression in G.lemaneiformis grown under low salinity(17‰)conditions for 1 week showed a slight increase in comparison with the control group(33‰ salinity,natural salinity of seawater),but the difference was not statistically significant(P>0.05);but when the culture time was extended to 2 weeks,the increase in both the agar yield and glugp expression became significant(P<0.01).However,phosphate limitation for 2 weeks had little effect on agar content and glugp expression(P>0.05).Our results suggest that glugp gene expression and agar content are highly positively correlated,and that the measurement of glugp expression,using only a small amount of thalli material,may be an efficient approach to evaluate agar content.In addition,both the agar content and glugp expression in cultivars 981,07-2 and ZC differed significantly from that of MT-18.The findings of this study suggest that UGPase may be involved in agar biosynthesis,and indicate that glugp gene expression could be a fairly reliable molecular marker to reflect the agar content of strains during breeding and selection of G.lemaneiformis.