The Molecular Basis Of The Evolution Of Stomatal Complex In Nymphaea Colorata

Originating over 400 million years ago,stomata is mainly distributed on the epidermis of plant leaves,stems,seeds and fruits.Stomata is critical for gas and water exchange between plants and the atmosphere,and plays a key role in plant transpiration and photosynthesis.Stomatal structure is highly conserved across land plants,the guard cells and the surrounding cells form a stomatal complex,the basic core structure with two guard cells surrounding the stomatal pore has stayed unchanged during evolution.However,the patterning of mature stomatal structure differs among plant groups,the diversed stomata structure,number,distribution and development have evolved and were renovated to facilitate the adaptation of plants to various environments.In the past,Arabidopsis thaliana was often used as model systems to study stomatal patterning and development.Based on those studies,we now have a good understanding of the basic molecular network behind stomatal development.In A.thaliana,stomata undergoes up to three asymmetrical divisions to form guard mother cell(GMC),then GMC undergoes symmetric mitosis to gives rise to dumb-bell guard cells.the distribution of stomata follows the principle of "cell to cell" on the leaf surface.In A.thaliana,a complex signaling cascade of several genes have been identified to promote stomatal development.The secreted peptides of the EPIDERMAL PATTERNING FACTOR(EPF)/EPF-LIKE(EPFL)family act with a mitogen-activated protein kinase(MAPK)cascade to regulate the activity of bHLH transcription factors.In the downstream,a number of mitogen-activated protein(MAP)kinases including MAPKKK YODA,MPKK4/5,MPKK7/9 and MAPK MPK3/6 were found to transduce the signaling for stomatal development.Five basic-helix-loop-helix(bHLH)transcription factors positively regulate the stomatal-lineage transition and differentiation.For example,SPEECHLESS(SPCH),MUTE,FAMA,act sequentially to promote cellular transition in a stage-specific manner.Two additional bHLH proteins,SCREAM and SCRM2,act redundantly to heterodimerize SPCH,MUTE and FAMA for coordinating the regulation.Although the molecular mechanism of stomata development in Arabidopsis has been widely studied,the evolution of stomata structure and its molecular regulators in different species remains to be answered.Nymphaea colorata is a member of ANITA-grade which is placed immediately above the root node of the angiosperms,and acts as a potential standard for understanding the evolutionary mechanism in more derived angiosperms.In this study,we examined the stomata development and the orthologs of Arabidopsis stomatal genes in a basal angiosperm plant N.colorata through bioinformatics.Our results showed the protodermal cells can directly become GMCs without asymmetrical division in N.colorata and GMCs divide symmetrically to produce GCs.Besides,we found that despite of the conservation of core stomatal regulators,a number of critical genes were lost the N.colorata genome,including the EPF2,MPK6,AP2C3 and the polarity regulator B ASL and POLAR.Interestingly,this is coincident with the loss of asymmetric divisions during stomatal development of N.colorata.Our analysis showed that although generally conserved,the loss of key regulatory genes associates with environmental adaptation of stomatal complex.