Analysis Of The Small Secreted Peptides In Reproductive Tissues Of Maize (Zea Mays)

Small secreted proteins are involved in plant growth and development, and stressresponses. Recent years, many small secreted peptides with important functions inreproduction have been found, such as ZmEA1, ZmES4in Maize. Maize is important cropand model plant. The study on the small secreted proteins is important for their research andapplication.In our study, we searched out the small secreted peptides of maize from the protein setpredicated from the database of genomic sequencing of B73inbred line based on thefollowing standards,(1) the number of amino acid is less than200;(2) including a singnalpeptide;(3) no transmembrane helix;(4) no ER lumen-resident sequence. We have found1732small secreted peptides of maize. With the help of Clastal X2, MEGA5, Claster3.0,NCBI, ExPasy, maizesequence, maizegdb, we analysised these small secreted peptides.These small secreted peptides were classified based on protein conserved domains,post-translation modification and the pattern of cystein arrangement. The set of small secretedpeptides was classified into195superfamilis. The number of different superfamily membersrange largly. The AAI LTSS superfamily had the most members,93. Yet there are93superfamilies have only1member each. No member belonging to RTFL, NCR in Maize wasidentified. There were6categories of post-translation modified small secreted peptides inArabidopsis. In Maize, only3categories of them, CLV3/CLE, PSK, and RGF, were identified,but CEP, PSY1and IDA was not identified. The small secreted peptides of Maize werecysteine, glycine, and leucine-rich, for example, the member of AAI LTSS, BAP, GASA andKnot1superfamilies harboring over4cysteine residues. The arrangements of cysteines inthese proteins shared the similar pattern with those in other plants，yet there are members ofAAI LTSS,GASA,BBI share different arrangements of cysteines with other plants.GO analysis revealed that the small secreted peptides of Maize play roles in thebiological progress such as signal transduction, reproduction, response to stimulates,biological regulation. About35%of the peptides could be classified into superfamilies involved in reproduction. Many of the small secreted peptides are high similarity in sequences.There are93peptides could be encoded by different transcripts or genes. The locations of thegenes encoding small secreted peptides showed change with their position at thechromosomes. The density of genes at the both ends of chromosomes is higher than that of atthe middle part. The PI of the small secreted peptides range largely, from3.39-12.40.However, the members of some superfamilies share similar PI. The PI of Knot1, GSSAsuperfamily member ranged from8-9,4-6of ML, PLA2-like, PSK superfamilies.The expression patterns of SSP genes of BAP, Knot1, Pollen Ole e I,RALF, Thioredoxinlike, RALF, SCP, SLR, Prolamin superfamilies in the development of reproductive organs ofmaize (developmenting silk, mature silk, developmenting ovary, mature ovary,developmenting tassel, mature pollen) were analyzed by qRT-PCR. Our results revealed thatthe genes of these SSPs showed high expression in the ovary and mature pollen.Sixty genes encoding small secreted peptides involved in the interaction between maleand female gametephytes were screen from the previous data. Four of them were expressed bysecreted yeast protein expressing system, grmzm2g039942p01, grmzm2g046532p01,grmzm2g397848p01, and grmzm2g483043p02. The crude peptides are absorbed with nickelcolumn, eluted with imidazole and then purified with ultrafiltration column. After treatment ofthe growing pollen tubes with the purified peptide in vitro, we found that grmzm2g397848p01could change the growth direction of pollen tube.