TaPHT1.2 is a functional,root predominantly expressed and low phosphate(Pi) inducible high-affinity Pi transporter in wheat,which is more abundant in the roots of P-efficient wheat genotypes(e.g.,Xiaoyan 54) than in P-inefficient genotypes(e.g.,Jing 411) under both Pi-deficient and Pi-sufficient conditions.To characterize TaPHT1.2 further,we genetically mapped a TaPHT1.2 transporter,TaPHT1.2-D1,on the long arm of chromosome 4D using a recombinant inbred line population derived from Xiaoyan 54 and Jing 411,and isolated a 1,302 bp fragment of the TaPHT1.2-D1 promoter(PrTaPHT1.2-D1) from Xiaoyan 54.TaPHT1.2-D1 shows collinearity with OsPHT1.2 that has previously been reported to mediate the translocation of Pi from roots to shoots.PrTaPHT1.2-D contains a number of Pi-starvation responsive elements,including P1BS,WRKY-binding W-box,and helix-loop-helix-binding elements.PrTaPHT1.2-D1 was then used to drive expression of β-glucuronidase(GUS) reporter gene in Arabidopsis through Agrobacterium-mediated transformation.Histochemical analysis of transgenic Arabidopsis plants showed that the reporter gene was specifically induced by Pi-starvation and predominantly expressed in the roots.As there is only one SNP between the TaPHT1.2-D1 promoters of Xiaoyan 54 and Jing 411,and this SNP does not exist within the Pi-starvation responsive elements,the differential expression of TaPHT1.2 in Xiaoyan 54 and Jing 411 may not be caused by this SNP.
Jun MiaoJinghan SunDongcheng LiuBin LiAimin ZhangZhensheng LiYiping Tong
Rice has a preference for uptake of ammonium over nitrate and can use ammonium-N efficiently. Consequently, transporters mediating ammonium uptake have been extensively studied, but nitrate transporters have been largely ignored. Recently, some reports have shown that rice also has high capacity to acquire nitrate from growth medium, so understanding the nitrate transport system in rice roots is very important for improving N use efficiency in rice. The present study identified four putative NRT2 and two putative NAR2 genes that encode components of the high-affinity nitrate transport system (HATS) in the rice (Oryza sativa L. subsp. japonica cv. Nipponbare) genome. OsNRT2.1 and OsNRT2.2 share an identical coding region sequence, and their deduced proteins are closely related to those from mono-cotyledonous plants. The two NAR2 proteins are closely related to those from mono-cotyledonous plants as well. However, OsNRT2.3 and OsNRT2.4 are more closely related to Arabidopsis NRT2 proteins. Relative quantitative reverse transcription-polymerase chain reaction analysis showed that all of the six genes were rapidly upregulated and then downregulated in the roots of N-starved rice plants after they were re-supplied with 0.2 mM nitrate, but the response to nitrate differed among gene members. The results from phylogenetic tree, gene structure and expression analysis implied the divergent roles for the individual members of the rice NRT2 and NAR2 families. High-affinity nitrate influx rates associated with nitrate induction in rice roots were investigated and were found to be regulated by external pH. Compared with the nitrate influx rates at pH 6.5, alkaline pH (pH 8.0) inhibited nitrate influx, and acidic pH (pH 5.0) enhanced the nitrate influx in 1 h nitrate induced roots, but did not significantly affect that in 4 to 8 h nitrate induced roots.
Chao CaiJun-Yi WangYong-Guan ZhuQi-Rong ShenBin LiYi-Ping TongZhen-Sheng Li
Abiotic stresses cause serious crop losses. Knowledge on genes functioning in plant responses to adverse growth conditions is essential for developing stress tolerant crops. Here we report that transgenic expression of MYB15, encoding a R2R3 MYB transcription factor in Arabidopsis thaliana, conferred hypersensitivity to exogenous abscisic acid (ABA) and improved tolerance to drought and salt stresses. The promoter of MYB15 was active in not only vegetative and reproductive organs but also the guard cells of stomata. Its transcript level was substantially upregulated by ABA, drought or salt treatments. Compared with wild type (WT) control, MYB15 overexpression lines were hypersensitive to ABA in germination assays, more susceptible to ABA-elicited inhibition of root elongation, and more sensitive to ABA-induced stomatal closure. In line with the above findings, the transcript levels of ABA biosynthesis (ABA1, ABA2), signaling (ABI3), and responsive genes (AtADH1, RD22, RD29B, AtEM6) were generally higher in MYB15 overexpression seedlings than in WT controls after treatment with ABA. MYB15 overexpression lines displayed improved survival and reduced water loss rates than WT control under water deficiency conditions. These overexpression lines also displayed higher tolerance to NaCl stress. Collectively, our data suggest that overexpression of MYB15 improves drought and salt tolerance in Arabidopsis possibly by enhancing the expression levels of the genes involved in ABA biosynthesis and signaling, and those encoding the stress-protective proteins.
Zhenhua DingShiming LiXueli AnXin LiuHuanju QinDaowen Wang
Phosphate (Pi) deficiency causes dramatic root system architecture(RSA) changes in higher plants.Here we report that overexpression of HRS1 leads to enhanced sensitivity to low Pi-elicited inhibition of primary root growth in Arabidopsis thaliana seedlings.Bioinformatic investigations uncovered that HRS1 and its six homologs encode putative G2-like transcription factors in Arabidopsis.Analysis of promoter::GUS reporter lines revealed that HRS1 transcripts were present mainly in the root hair region and root hair cells under Pi-sufficient conditions.Pi deprivation increased HRS1 expression level and expanded its expression domain.Although HRS1 knockout mutant did not differ from wild type(WT) control irrespective of Pi status,its overexpression lines were significantly more susceptible to low Pi-elicited primary root shortening.In both WT and HRS1 overexpression seedlings,low Pi-induced primary root shortening was accompanied by enhanced root hair cell differentiation,but this enhancement occurred to a greater extent in the latter genotype.Collectively,our data suggest that HRS1 may be involved in the modulation of primary root and root hair growth in Pi-deprived Arabidopsis seedlings,and provide useful clues for further research into the function of HRS1 and its homologs and the mechanisms behind RSA changes under Pi-deficient conditions.
Hong LiuHuixia YangChongming WuJuanjuan FengXin LiuHuanju QinDaowen Wang
Wheat is a staple food crop in the world as well as in China. Because of the progress of wheat breeding and other agricultural sci-technologies, the wheat grain yield per unit area has increased more than five folds from 1952 to 2006 in China. The first part of this article briefly reviews the history of wheat breeding in China. Second, the establishment of "Triticum aestivum-Agropyron" distant hybridization system and its contribution to wheat production and breeding in China are summarized. Finally, the future challenges of wheat breeding are discussed, which include how to increase the utilization efficiencies of water, soil nutrient and light energy through breeding. As an example, our research progress on how to increase light use efficiency in wheat through breeding is introduced and discussed.
