周玉乾，孟思遠(yuǎn)，周文期(.甘肅省農(nóng)業(yè)科學(xué)院 作物研究所，蘭州 730070； .甘肅省種子管理局，蘭州 73000)

植物表皮在組織器官的生長(zhǎng)發(fā)育和形態(tài)建成中發(fā)揮非常重要的作用[1-3]。表皮是植物體內(nèi)與外界環(huán)境的天然保護(hù)屏障，它不僅可以感知外界刺激、傳遞信號(hào)，吸收營(yíng)養(yǎng)等，而且表皮細(xì)胞外壁常覆蓋一層脂肪性物質(zhì)，稱角質(zhì)層，在植物的地上器官(如莖、葉、花、果實(shí)和種子)中具有保護(hù)功能[4-6]。增加表皮層厚度不僅能使植物有效地抵御外界有機(jī)脅迫(微生物、病蟲害侵襲)和無(wú)機(jī)脅迫(低溫、高鹽堿等)，更能減少植物體內(nèi)熱量及水分的散失[7]；在地下器官(根)中具有吸收功能。因此，研究植物表皮的分裂、分化與形態(tài)建成對(duì)植物的正常生長(zhǎng)發(fā)育具有非常重要的理論意義。植物葉表皮扁平細(xì)胞排列緊密，細(xì)胞邊緣凸凹嵌套，沒(méi)有細(xì)胞間隙(除了氣孔)。除一般的表皮扁平細(xì)胞外，葉表皮細(xì)胞還包括特化的氣孔復(fù)合體和表皮毛等附屬物，在禾本科植物葉中還包括泡狀細(xì)胞、以及由硅質(zhì)細(xì)胞和栓質(zhì)細(xì)胞緊密鑲嵌而成的短細(xì)胞[8-10]。近幾年來(lái)，隨著生物技術(shù)的不斷提高，對(duì)植物表皮形態(tài)建成的研究成為一大熱點(diǎn)，尤其在雙子葉模式植物擬南芥中，取得了一系列的研究成果，但是在單子葉植物中，調(diào)控氣孔及表皮細(xì)胞發(fā)育圖式的基因及參與分子調(diào)控網(wǎng)絡(luò)的機(jī)理研究非常受限，因此需要更多科技工作者去深入探討和研究。

1 雙子葉植物葉表皮扁平細(xì)胞及表皮毛形態(tài)建成及分子機(jī)制

植物表皮主要作用是增加表皮層的厚度，減少熱量及水分散失，從而保護(hù)表皮層下組織，以免受到病蟲侵害及機(jī)械傷害[7]。擬南芥(Arabidopsisthaliana) 作為一種雙子葉植物的模式植物，對(duì)其葉表皮的研究已經(jīng)取得很大的進(jìn)展。研究證明，擬南芥葉表皮扁平細(xì)胞的發(fā)育經(jīng)歷3個(gè)階段：第1階段，表皮原始細(xì)胞先沿著葉長(zhǎng)軸開始擴(kuò)展，形成稍微變長(zhǎng)的多變形細(xì)胞；其次，沿細(xì)胞壁的背斜面向鄰近細(xì)胞側(cè)面延伸，細(xì)胞邊緣逐漸形成不規(guī)則的鋸齒狀凸出(lobe)；最后，細(xì)胞凸出進(jìn)一步向外延伸，與相鄰細(xì)胞狹窄的凹陷(neck) 處交錯(cuò)相連，最終形成復(fù)雜多變的表皮圖式[11]。擬南芥表皮毛是一種特化的、典型的單細(xì)胞結(jié)構(gòu)，一般有3個(gè)分支，無(wú)腺體，廣泛分布于葉、莖、花瓣的表面。其發(fā)育過(guò)程包括起始發(fā)育、分支、延伸和形態(tài)建成4 個(gè)階段[12]。葉表皮不規(guī)則的齒狀凸出和頸的形成以及表皮毛的延伸與發(fā)育主要受細(xì)胞骨架(微管，微絲和中間纖維)的調(diào)控。微管主要調(diào)控葉扁平細(xì)胞延伸與分裂[1,13]。微管結(jié)合蛋白MAP65(microtubule associated protein 65) 負(fù)責(zé)微管穩(wěn)定以及微管成束[14]；微管切割蛋白KTN1(katanin 1) 與植物中的小G蛋白R(shí)OPs(rho-like small GTPase in plant) 的效應(yīng)蛋白R(shí)IC1(ROP-interactive CRIB motif-containing protein 1)結(jié)合，通過(guò)切割微管進(jìn)而調(diào)控微管的分布[15]；Rho-GTPase級(jí)聯(lián)信號(hào)通路能調(diào)控微管與微絲的排列，從而導(dǎo)致葉扁平細(xì)胞形態(tài)改變[11,16]。微絲主要控制表皮細(xì)胞邊緣的凸出，即lobe的形成和圖式發(fā)育[2,11,17-18]。微絲結(jié)合蛋白ABPs(Actin binding proteins) 調(diào)節(jié)微絲的聚合以及微絲動(dòng)態(tài)裝配[19]；目前已被證實(shí)的擬南芥中微絲結(jié)合蛋白主要包括：微絲解聚因子(actin-depolymerizing factors)、前纖維蛋白(profilin)、肌動(dòng)蛋白(fimbrins)、絨毛蛋白(villin)、肌動(dòng)蛋白相關(guān)蛋白Arp2/3(actin-related protein 2/3) 復(fù)合體等都參與細(xì)胞的形態(tài)發(fā)生[20-21]。

在擬南芥中已經(jīng)證明參與調(diào)控扁平細(xì)胞及表皮毛發(fā)育有多條信號(hào)通路，表皮毛的形態(tài)和發(fā)育的調(diào)控均依賴相關(guān)基因的精確表達(dá)，其中大部分屬于R2R3類型的MYB、bHLH(basic helix-loop-helix)和含WD40重復(fù)序列的TTG(RANSPARENTTESTA GLABRA1) 類轉(zhuǎn)錄因子，表皮毛發(fā)育及分子調(diào)控目前研究比較清晰[22-28]。本研究就針對(duì)依賴于SPK1-ROPs-SCAR/WAVE-ARP2/3這一信號(hào)通路進(jìn)行介紹，該通路基因通過(guò)調(diào)控微絲核化改變細(xì)胞骨架結(jié)構(gòu)，從而導(dǎo)致葉扁平細(xì)胞及表皮毛發(fā)育過(guò)程形態(tài)異常，該通路成員有SPK1(spike 1)，ROPs，環(huán)磷酸腺苷受體結(jié)合抑制因子SCAR/WAVE(suppressor of cAMP receptor/ Wiskott-Aldrich syndrome protein-family verprolin-homologous protein) 復(fù)合體，ARP2/3復(fù)合體[22,29-30]。單突變體spk1表皮毛分支明顯減少，不規(guī)則，扭曲延伸，扁平細(xì)胞邊緣凸出減少[3,31]。ROP家族在擬南芥中共有11個(gè)成員，分別是ROP1～ROP11，其中ROP1～ROP6主要調(diào)控細(xì)胞極性生長(zhǎng)，參與葉表皮細(xì)胞形態(tài)建成，組成激活突變體CA-rop2扁平細(xì)胞顯著膨大，非極性分裂生長(zhǎng)，表皮毛表現(xiàn)出腫脹表型，分枝不規(guī)則，扭曲；而負(fù)顯性突變體DN-rop2扁平細(xì)胞狹窄，lobe變短[32]。ROP2/4在扁平細(xì)胞lobe頂端質(zhì)膜上激活，促進(jìn)RIC4-依賴的皮層微絲積累，促進(jìn)了細(xì)胞向外凸出生長(zhǎng)，控制微絲聚集，而ROP6在neck區(qū)域與RIC1結(jié)合促進(jìn)微管的裝配，進(jìn)而抑制細(xì)胞凸出形成[11]。ROPs信號(hào)分子在該通路中起“開關(guān)”作用，另一通路就是激活下游SCAR/WAVE復(fù)合體，繼續(xù)信號(hào)傳遞[33-34]。SCAR/WAVE 復(fù)合體共包括5個(gè)亞基，分別是PIR/SRA1(PIROGI/Specifically Rac1-associated protein)NAP1/NAP125(NCK-associated protein)，BRICK1/HSPC300(haematopoietic stem progenitor cell 300)，ABI(abl-interactor 2) 和 SCAR/WAVE[35-37]。研究證明，該復(fù)合體中PIR/SRA1亞基接收上游ROPs的激活信號(hào)，SCAR/WAVE亞基與下游ARP2/3復(fù)合體直接相互作用并激活下游信號(hào)通路[36-40]。該復(fù)合體中單突變體pir1、nap1、brk1、wave1等都呈現(xiàn)出表皮毛扭曲，分枝不規(guī)則表型，并且細(xì)胞粘連處有缺口，細(xì)胞排列不緊密，brk1扁平細(xì)胞邊緣突出變平滑的表型更為明顯[21,37,41-42]。Arp2/3復(fù)合體由7個(gè)亞基構(gòu)成，分別是ARP2、ARP3、ARPC1-ARPC5[43-44]。4種稱為“變形(distorted)”基因分別編碼ARP2、ARP3、ARPC2以及ARPC5，單個(gè)基因突變同樣表現(xiàn)出表皮毛扭曲、腫脹，分枝繚亂，長(zhǎng)度減少等表型[45-47]。大量試驗(yàn)證明編碼該信號(hào)通路的蛋白功能相對(duì)保守，SCAR/WAVE和ARP2/3復(fù)合體主要通過(guò)調(diào)節(jié)微絲斑或微絲帶的形成來(lái)調(diào)控細(xì)胞極性生長(zhǎng)過(guò)程，從而改變?nèi)~扁平細(xì)胞以及表皮毛的形狀[36,48]。目前雙子葉植物中，對(duì)通過(guò)微管和微絲調(diào)控?cái)M南芥表皮細(xì)胞的圖式發(fā)育和形態(tài)建成的信號(hào)通路研究取得較大的成果。

2 雙子葉植物中氣孔的圖式發(fā)育及分子機(jī)制

氣孔是高等植物表皮上的一種特化結(jié)構(gòu)，是蒸騰過(guò)程中水蒸氣從體內(nèi)排到體外的主要出口，也是光合作用和呼吸作用與外界氣體交換的“大門”，對(duì)植物的蒸騰、光合、呼吸等都起著非常重要的作用。氣孔在調(diào)節(jié)植物逆境環(huán)境中，常通過(guò)其開關(guān)來(lái)維持體內(nèi)水分，在維持地球水分平衡、碳氧平衡及植物的生命活動(dòng)中均發(fā)揮著非常重要的作用[49-50]。當(dāng)光照、溫度、CO2含量、葉片含水量、化學(xué)物質(zhì)等環(huán)境因子發(fā)生變化時(shí)，植物通過(guò)調(diào)整氣孔孔徑大小來(lái)控制自身與外界的氣體交換能力，以便能更好地適應(yīng)外界環(huán)境[50-51]。擬南芥的原表皮細(xì)胞同時(shí)具有發(fā)育成扁平細(xì)胞、氣孔和表皮毛的能力。原表皮細(xì)胞逐漸發(fā)育成擬分生組織母細(xì)胞MMC(meristemoid mother cell)，屬于氣孔干細(xì)胞，并主導(dǎo)氣孔系細(xì)胞的第1次不均等起始分裂，產(chǎn)生2個(gè)子細(xì)胞，小細(xì)胞為擬分生組織(meristemoid)，繼續(xù)進(jìn)行細(xì)胞不均等分裂，或者分化為保衛(wèi)細(xì)胞母細(xì)胞GMCs(guard mother cells)；其中較大的姊妹細(xì)胞稱為氣孔系基礎(chǔ)細(xì)胞SLGC(stomatal lineage ground cell)，發(fā)育成扁平細(xì)胞PCs(pavement cells)，GMCs再進(jìn)行一次均等分裂，進(jìn)而最終分化成2個(gè)保衛(wèi)細(xì)胞GCs(guard cells)，細(xì)胞壁加厚，逐漸形成孔狀特化的氣孔結(jié)構(gòu)。氣孔擬分生組織在發(fā)育過(guò)程中，經(jīng)歷1～3次不均等分裂形成氣孔和多個(gè)扁平細(xì)胞[49]。把這種經(jīng)過(guò)1～3次不均等分裂過(guò)程稱為氣孔系細(xì)胞的擴(kuò)增分裂(amplifying division)；把另一種氣孔系基礎(chǔ)細(xì)胞重新獲得分裂能力，形成2個(gè)氣孔和1個(gè)扁平細(xì)胞的分裂稱為空間分裂(spacing division)，這2種分裂模式同時(shí)調(diào)控氣孔在表皮層的分布和發(fā)育，使氣孔分布遵循“一個(gè)氣孔間隔一個(gè)扁平細(xì)胞”交錯(cuò)的排列模式[49,52-53]。

擬南芥中有關(guān)氣孔發(fā)育及調(diào)控機(jī)理有比較深入的研究，其信號(hào)通路主要包括轉(zhuǎn)錄因子，配體與受體、MAPK信號(hào)級(jí)聯(lián)等[54-55]。已經(jīng)報(bào)道了3個(gè)bHLH正調(diào)轉(zhuǎn)錄因子SPCH(Speechless)、MUTE 和FAMA，分別與另2種轉(zhuǎn)錄因子SCRM/ICE1(Scream/inducer of cbf expression 1) 和SCRM2(scream 2)形成異二聚體，分別調(diào)控由原表皮細(xì)胞向擬分生組織，擬分生組織向保衛(wèi)細(xì)胞母細(xì)胞，以及保衛(wèi)細(xì)胞母細(xì)胞向保衛(wèi)細(xì)胞的分裂與分化3個(gè)關(guān)鍵過(guò)程[56-59]；RNA聚合酶Ⅱ第3大亞基NRPB3(the third largest subunit of RNA polymerase Ⅱ) 能夠與FAMA和ICE1相互作用，來(lái)執(zhí)行氣孔發(fā)育和圖式分化特異的轉(zhuǎn)錄調(diào)控，功能缺陷型突變體nrpb3-1表現(xiàn)出2個(gè)氣孔系細(xì)胞簇生的表型，包括簇生擬分生組織、GMCs和氣孔復(fù)合體[60]。另外，MYB 轉(zhuǎn)錄因子主要包括FLP(FOUR LIPS) 和 MYB88,編碼2種R2R3類 MYB 蛋白，與FAMA獨(dú)立協(xié)同調(diào)控GMCs 向GCs的分化和轉(zhuǎn)變，在此過(guò)程中，F(xiàn)AMA須結(jié)合另一種叫作RBR(RETINO BLASTOMA RELATED) 蛋白才能行使功能，均在氣孔形成晚期發(fā)揮重要的調(diào)控作用[56,61-62]。配體主要包括表皮模式因子EPFs(epidermal patterning factors) 家族EPF1、EPF2、EPFL5、EPFL6負(fù)調(diào)控氣孔發(fā)育，STOMAGEN/EPFL9則對(duì)氣孔發(fā)育起正調(diào)節(jié)作用[63-65]。受體包括富亮氨酸重復(fù)區(qū)受體類激酶(LRR-LRK) 包括ERECTA家族成員[ER、ERL1(ERECTA LIKE 1) 和ERL2]，以及SERK(SOMATIC EMBRYOGENESIS RECEPTOR KINASE) 家族成員SERK1-SERK4，與其共受體富亮氨酸重復(fù)的受體類蛋白TMM(TOO MANY MOUTH) 共同調(diào)控氣孔系前體細(xì)胞的不均等分裂；植物促分裂原蛋白活化激酶級(jí)聯(lián)信號(hào)MAPK信號(hào)級(jí)聯(lián)(MAPK signaling cascade) 由促分裂原蛋白活化激酶YODA/MAPKKK、MKK4/MKK5/MKK7/MKK9和MPK3/MPK6構(gòu)成，YODA-MKK4/5-MPK3/6信號(hào)級(jí)聯(lián)通路中激酶的功能缺失導(dǎo)致葉表皮形成氣孔簇，而持續(xù)激活將導(dǎo)致葉片沒(méi)有氣孔的形成[66-68]，因此，不同的酶活性水平影響氣孔系細(xì)胞的正常發(fā)育。此外，一個(gè)新的受體蛋白BASL(BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE) 也調(diào)控氣孔系擬分生組織母細(xì)胞和擬分生組織細(xì)胞的不均等分裂[69-70]?？莶輻U菌蛋白酶類的絲氨酸蛋白酶SDD1(STOMATAL DENSITY AND DISTRIBUTION1) 作用于TMM上游，在擬分生組織細(xì)胞和GMCs中表達(dá)，調(diào)控氣孔圖式發(fā)育[71-72]。

3 單子葉植物氣孔及扁平細(xì)胞發(fā)育圖式形成研究進(jìn)展

雖然有關(guān)葉扁平細(xì)胞和氣孔的研究在擬南芥中取得的進(jìn)展令人鼓舞，但在玉米(ZeamaysL.)和水稻(OryzasativaL.) 等單子葉植物中，調(diào)控氣孔及表皮細(xì)胞生長(zhǎng)發(fā)育與形態(tài)建成的分子機(jī)制研究非常受限，因此亟待研究者去發(fā)現(xiàn)和挖掘。

單子葉植物中葉氣孔及表皮細(xì)胞的生長(zhǎng)發(fā)育、排列方式等與雙子葉植物中截然不同[73]。在雙子葉植物中，雖然2個(gè)氣孔遵循間隔1個(gè)扁平細(xì)胞的排列模式，但是氣孔雜亂無(wú)章地分布在葉表皮上，并且在成熟葉片中，處于各種分裂與分化狀態(tài)的氣孔和扁平細(xì)胞形態(tài)隨時(shí)能被觀察到。但是在單子葉禾本科植物中，氣孔一列列整齊地排列在葉脈兩側(cè)，也遵循2個(gè)氣孔間隔1個(gè)扁平細(xì)胞的排列模式[8]。早期葉原基形成后，氣孔系細(xì)胞便開始分裂與分化，并在較短時(shí)間內(nèi)完成發(fā)育，因此在成熟葉片中，幾乎觀察不到正處于分裂或者分化的氣孔系細(xì)胞[73-74]。玉米葉氣孔及扁平細(xì)胞的發(fā)育過(guò)程與水稻中基本一致[75]，氣孔都是由氣孔系原始細(xì)胞(也叫保衛(wèi)細(xì)胞母細(xì)胞前體細(xì)胞)進(jìn)行第1次不等分裂，產(chǎn)生2個(gè)大小不一的子細(xì)胞，大細(xì)胞直接發(fā)育成PCs，而小細(xì)胞稱為GMCs，GMCs具有氣孔系干細(xì)胞命運(yùn)，能繼續(xù)分裂與分化；當(dāng)位于GMCs兩側(cè)的副衛(wèi)細(xì)胞母細(xì)胞SMCs(subsidary mother cells) 接收到GMCs傳遞的某種信號(hào)后，起初在GMCs 和SMCs 接觸的位置形成微絲斑，然后SMCs的細(xì)胞核朝GMCs極化進(jìn)行第2次不均等分裂，形成副衛(wèi)細(xì)胞SCs(subsidary cells)；最后，GMCs 再進(jìn)行1次橫向均等分裂，形成對(duì)稱的2個(gè)保衛(wèi)細(xì)胞，隨著葉發(fā)育成熟，最終形成由2個(gè)三角形狀的副衛(wèi)細(xì)胞夾著2個(gè)啞鈴狀的保衛(wèi)細(xì)胞組成的氣孔復(fù)合體[76-79]。

目前研究發(fā)現(xiàn)，無(wú)論在雙/單子葉植物中，氣孔的分化均受到一類bHLH 家族轉(zhuǎn)錄因子的調(diào)控，主要包括SPCH、MUTE和FAMA[77]。在水稻中， OsSPCH2調(diào)控氣孔形態(tài)及氣孔密度，OsFAMA主要控制極性分裂及副衛(wèi)細(xì)胞的形態(tài)變化，與ATFAMA功能保守，調(diào)控GMCs向特化GCs分裂。擬南芥中過(guò)表達(dá)OsMUTE氣孔缺陷表型得到部分恢復(fù)，過(guò)表達(dá)ZmMUTE，也能誘導(dǎo)產(chǎn)生很多的保衛(wèi)細(xì)胞，因此，推測(cè)在玉米中，同源蛋白ZmSPCH、ZmMUTE和ZmFAMA都參與調(diào)控氣孔系細(xì)胞發(fā)育的信號(hào)通路[77]。玉米中富亮氨酸受體類激酶PAN1(PANGLOSS1) 和PAN2 作為受體識(shí)別來(lái)源于GMCs 傳遞的信號(hào)，調(diào)控SMCs的不均等分裂方向及其子細(xì)胞的極性分裂，功能缺失均導(dǎo)致氣孔及表皮細(xì)胞結(jié)構(gòu)異常，PAN2可能參與微絲極化，影響副衛(wèi)細(xì)胞的形狀，基因突變后能引起三角形的副衛(wèi)細(xì)胞變成矩形[76,80-81]。Rho家族GTPase、ROP2和ROP9與PAN1互作，調(diào)控SMCs的極性分裂[82]。在單子葉植物二穗短柄草中，STOMATALESS(STL) 基因功能缺失導(dǎo)致葉片中不能形成氣孔，并且證明STL基因就是擬南芥與水稻中ICE的同源基因[83]。同時(shí)他們利用CRISPR-Cas 9(clustered,regularly interspaced short palindromic repeats-associated 9) 基因編輯技術(shù)，分離到bdscrm2突變體，研究表明BdSCRM2功能缺陷，雖然能形成GMCs和SCs，但是GMCs將不能正常分裂，成為開孔。雙突變體 bdspch1、bdspch2和 bdice1的突變體在氣孔發(fā)育早期均不能形成GMCs前體細(xì)胞，導(dǎo)致氣孔密度顯著降低，這表明 BdSPCHs 和 BdICE1 的功能與擬南芥中的氣孔調(diào)控比較相似，在調(diào)控氣孔系細(xì)胞早期發(fā)育中發(fā)揮作用[83]。因此筆者推測(cè)在水稻及玉米等禾谷類作物中，同源蛋白ZmSPCHs(3個(gè))、ZmICE1、ZmICE2、OsICE1和OsSCRM2等也參與氣孔系細(xì)胞的分裂與分化，這有待更多的學(xué)者進(jìn)行基因功能的研究，以期闡明調(diào)控單子葉植物氣孔系細(xì)胞形態(tài)建成的內(nèi)在基因調(diào)控網(wǎng)絡(luò)。

對(duì)玉米及水稻中調(diào)控葉扁平細(xì)胞形態(tài)和表皮毛的基因，推測(cè)主要依賴Racs(ROPs)-SCAR/WAVE-ARP2/3復(fù)合體這一保守的信號(hào)通路[79]。在玉米中，早期報(bào)道了3個(gè)BRK(Brick)基因通過(guò)調(diào)控微絲成核，影響微絲排列而導(dǎo)致葉表皮細(xì)胞邊緣突出(lobe) 的缺失，且表皮毛變短、尖端變鈍化[84-85]。由于當(dāng)時(shí)基因組信息的不完善，文章沒(méi)有給出具體的基因座信息，更沒(méi)有提出這3個(gè)基因就是WAVE復(fù)合體中的3個(gè)亞基，但是筆者通過(guò)生物信息學(xué)比對(duì)和分析，確定BRK1、BRK2和BRK3與擬南芥中HSP300、PIR/SRA1和NAP1就是相互對(duì)應(yīng)的同源蛋白，且進(jìn)化上功能保守，通過(guò)調(diào)控微絲成核分別引起葉表皮細(xì)胞形態(tài)變化[79,84-85]。在水稻中，表皮毛禿頭基因 TUTOU1/ES1(Early Senescence 1)編碼擬南芥及玉米SCAR1同源蛋白，通過(guò)控制微絲合成，影響表皮毛的形態(tài)發(fā)育，表皮毛尖端鈍化，并證明功能缺失突變體 es1對(duì)干旱等逆境脅迫更敏感[86-87]。ZHOU等[79]在水稻中克隆了2個(gè)調(diào)控表皮細(xì)胞形態(tài)建成基因LPL2(less pronounced lobe epidermal cell 2) 和LPL3，分別是玉米BRK2和BRK3及擬南芥中PIR/SRA1和NAP1的同源基因，并證明LPL2和LPL3在調(diào)控水稻葉表皮細(xì)胞邊緣凸出中發(fā)揮不可或缺的功能，同屬于水稻SCAR/WAVE復(fù)合體的亞基，酵母雙雜交試驗(yàn)表明LPL2和LPL3能夠相互作用[88]。總之，雖然在單子葉植物中，也克隆到少數(shù)幾個(gè)調(diào)控葉表皮細(xì)胞圖式發(fā)育的基因，但是離闡明單子葉植物葉表皮形態(tài)建成機(jī)制仍相差甚遠(yuǎn)，亟待挖掘。

4 展 望

目前，對(duì)單子葉植物水稻、玉米葉表皮發(fā)育的遺傳調(diào)控機(jī)制還懸而未決，單子葉植物氣孔及扁平細(xì)胞的發(fā)育機(jī)制不等同于雙子葉植物，新的分子遺傳調(diào)控機(jī)制方面的許多問(wèn)題亟待解決：(1)氣孔方面：有哪些特異性基因參與調(diào)控單子葉植物氣孔系細(xì)胞的分裂與分化？氣孔發(fā)育圖式是如何相互調(diào)控的？(2)表皮細(xì)胞方面：水稻及玉米等單子葉植物中是否存在依賴ROPs-SCAR/WAVE-ARP2/3復(fù)合體調(diào)控表皮細(xì)胞形態(tài)建成的信號(hào)通路？如果存在，分別由哪些亞基組成？各自的功能又是什么？還有哪些信號(hào)通路參與其中[79]？等等問(wèn)題亟待探索和研究。

植物表皮細(xì)胞發(fā)育過(guò)程易于顯微觀察，是研究植物的生長(zhǎng)發(fā)育、細(xì)胞分裂與分化、形態(tài)建成和抗逆生理性研究的理想模型[49]?？寺≌{(diào)控氣孔發(fā)育相關(guān)基因、解析并研究基因功能，增進(jìn)對(duì)水稻玉米等糧食作物氣孔和表皮細(xì)胞發(fā)育機(jī)制的認(rèn)識(shí)，可以通過(guò)轉(zhuǎn)基因及基因編輯等分子育種手段選育既能節(jié)約淡水灌溉，又能促進(jìn)農(nóng)作物增產(chǎn)的優(yōu)良品種的選育，對(duì)作物改良具有重大意義。

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