Differential expression of PAL multigene family in allelopathic rice and its counterpart exposed to stressful conditions

As an ecological weed control method,allelopathy is considered a potential sustainable approach for controlling weed population in the 21st Century.Therefore it has received increasing attention.Our previous studies showed that the allelopathic effect on the target weed,barnyardgrass,was enhanced when the allelopathic rice cultivar PI312777 was exposed to limited nutrient conditions.Furthermore,the enzymatic activities of protective enzymes increased,and the expression of genes associated with phenylpropanoid metabolism was also up-regulated.This activated phenylpropanoid metabolism functions in the de novo synthesis of allelochemicals,and hence increases the contents of phenolic allelochemicals contributing to stronger ability of the allelopathic rice to suppress the target weeds.It was also found that the alleopathic potential of rice was dependent mainly on the species and content of allelochemicals produced in phenylpropanoid metabolism pathway.Activation of genes encoding key enzymes participated in the phenylpropanoid pathway leads to increased releases of allelochemicals,and in turn suppresses growth of accompanying weeds in hydroponics.Activation of these genes can be regulated by various biotic or abiotic factors.The phenomena complicate the elucidation of the underlying mechanism.Further understanding of the functional genes of allelopathic rice in regulating the adaptation of plants to stressful conditions will help explore a possible method of enhancing rice allelopathic potential through biotechnology.The ubiquitous higher plant enzyme phenylalanine ammonia-lyase(PAL) is the first key biosynthetic catalyst in phenylpropanoid assembly,which catalyses the non-oxidative deamination of L-phenylalanine to trans-cinnamic acid and regulates phenylpropanoid biosynthesis.PAL is encoded by a small multigene family;the gene transcript level of PAL is responsive to a variety of environmental stimuli including nutrient deficiency,UV irradiation,pathogen infection,wounding,extreme temperatures and other stress conditions.Silenced or disrupted PAL genes result in retarded plant growth and development as well as responses to environmental stresses.Rice contains at least 11 individual PAL genes and is regulated by various environment factors.The present study was to identify the specific members of the PAL family that regulate allelopathy in rice.Specific primers for each putative PAL gene were designed by the Primer Premier 5.0 software.And,the real time quantitative PCR(qRT-PCR) was used to investigate the differential expression patterns of 11 PAL genes in allelopathic rice PI312777 and its courtpart,Lemont.The result showed that a detectable amplification product was obtained for 9 genes out of 11,and 9 of the PAL genes,which were differentially expressed.Among them,PAL11 was up-regulated in the two rice accessions,with 3.29-and 1.07-folds up-regulation in PI312777 and 3.92-and 1.08-folds up-regulation in Lemont when exposed to lower nitrogen and high density of barnyardgrass stress,respectively.PAL3 and PAL9 were only up-regulated in PI312777,with 1.83 and 2.66 folds under lower nitrogen condition,and 1.46 and 2.65 folds under barndyardgrass stress condition respectively.These two genes were down-regulated in Lemont under same stress conditions,with 1.05-fold for PAL3 and 1.24-fold for PAL9 under nitrogen deficiency and 1.14-and 1.16-folds for PAL3 and PAL9,respectively,under barndyardgrass stress condition.No expression of PAL4 and PAL10 was detected in the two rice accessions under the same stressful conditions.The findings suggested that PAL3 and PAL9 genes may participate in regulating allelopathic potential of allelopathic rice in early stress response.