Functional Analysis Of OsYSL15 And OsYSL16 In Rice Microelements Distribution

Essential microelements,including iron(Fe),copper(Cu),zinc(Zn)and manganese(Mn),play critical roles in plant physiological processes,such as photosynthesis,respiration,nitrogen assimilation,hormone and protein biosynthesis,generation and elimination of reactive oxygen species,and pathogen defense.In order to satisfy the need of nutrition,plants have been developed a complex system for microelements absorption,translocation and distribution.Many transporters including YSL family members,were involved in it.Recent reports show that rice YSLs take part in many trace elements homeostasis.However,the nutrients distribution mechanisms in many processes are largely unknown.It has been reported that OsYSL15 and OsYSL16 were involved in Fe-deoxymugineic acid(DMA)absorption in roots and Cu-nicotianamine(NA)distribution from old leaves to the new ones as well as flag leaves to spikelet.respectively.OsYSL15 was not only expressed in root epidermis,but also expressed in root stele.Besides,OsYSL16 was not only expressed in vascular bundles of leaves and node I,but also expressed in floral organs.In this study,we analyzed the function of OsYSL15 and OsYSL16 in rice microelements distribution.Main results are as follows.Os YSL has 18 members which are divided into four sub-groups.OsYSL genes are distributed on five chromosomes,including chromosomes 1,2,4,5 and 8.All OsYSL genes family members are composed of exon and intron.Members in the same subfamily share a similar gene structure.All members are predicted to contain numerous transmembrane domains,which can suit with the function of microelements translocation.The numbers and positions of transmembrane domains in different members are not all the same,intimating that they may play different functions in microelements translocation.Subcellular localization prediction results show that all Os YSLs members are located in plasma membrane,suggesting that OsYSLs may not be involved in vacuole storage.OsYSL2,9,13,15 and 16 are induced by Fe deficiency.OsYSL15 is induced most highly among them,indicating that it may play an important role in Fe homeostasis.There was no significantly increased expression of OsYSLs under Zn,Mn and Cu deficient treatments.OsYSL genes family members can be clustered into two groups,which were based on the expression level in different tissues or organs.One group has a higher expression level,while the other group has a lower one.Besides nutrition organs,OsYSLs are also expressed in reproduction organs.It seems that OsYSLs may also be required for microelement translocation of reproduction organs.For example,OsYSL5,6,7,14 and 16 both have a high expression level in reproduction organs.All the results imply that OsYSLs have complex and diverse physiological functions in microelement homeostasis.Fe is important for most living organisms.It is necessary to improve the utilization of Fe effectively.However,the exact mechanism of Fe root to shoot translocation in rice is still unclear.In this study,OsYSL15 was selected to investigate it.OsYSL15 was mainly expressed in root and induced by Fe deficiency.The expression level of OsYSL15 in stele was similar with that in epidermis.Moreover,GUS staining results show that it is mainly expressed in root pericycle under Fe sufficient condition.The growth of osysl15 was inhibited more seriously than wild type at 0.2 ?M FeSO4.Reduced Fe concentrations in shoot and xylem were found in osysl15 at each FeS?4 concentrations used in this paper.Opposite results were found in OX-OsYSL15 lines.In addition,more Fe was accumulated out of the pericycle in osysl15 compared with wild type.Genes involved in Fe homeostasis were induced in the root of osysl15 at 0.2 ?M FeSO4 and OsYSL2 was induced most highly of all.Thus,OsYSL15 takes part in Fe translocation from root to shoot.Flower is necessary for fertility,yield and quality of rice.However,transporters for microelements distribution in floral organs have not been identified.In addition,the correlation between proper Cu distribution in floral organs,pollen viability and fertility in rice is still poorly understood.Here,we reported that OsYSL16 was essential in the Cu distribution and redistribution in rice floral organs.OsYSL16 was highly expressed in palea.lemma and highest in rachilla among floral organs.GUS staining of-OsYSL16 promoter-GUS transgenic rice showed that OsYSL16 was mainly expressed in center vascular bundles and vascular bundles connected with palea and lemma in rachilla,and in vascular bundles of palea and lemma.A decreased Cu distribution rate in stamens and increased ones in palea and lemma have been found in osysl16.Isotope tracer experiment showed that osysll6 had higher Cu concentrations in palea and lemma compared with wild type.Besides,the Cu mobility of the palea and lemma in the wild-type rice and two complementation lines were higher after Cu deficiency than that in the mutant line.In addition to decreased pollen viability,reduced pollen germination rates both in vivo and in vitro were detected in osysl16.However,no structural difference of pollen grains was found between osysl16 and wild type by using transmission electron microscopy.As a result,osysl16 has a lower fertility and thousand grains weight compared with wild type and two independent complementation lines.Therefore,OsYSL16 was required for proper Cu distribution of floral organs and pollen germination which is important for rice fertility.In conclusion,we found that OsYSL15 played a critical role in Fe translocation from root to shoot and OsYSL16 was essential for Cu distribution in floral organs.And lower Cu concentration in stamens can affect pollen germination rates.