| Cotton is one of the most important crops in the world. It’s products are veryvaluable. It is not only an important oil crop, but also an important fiber crop.What’s more,it has a high protein content. Therefore, cotton is supposed to be the best raw materials andstrategic materials for textile and chemical industry.However, cotton itself has complexbranch mode and growth habit, which cause a lot of labor cost for pruning and shoot apexremoving. Therefore, it is very important to conduct research on the cotton branch.GhMAX2belongs to the F-box/LRR protein family, showing high homology with theArabidopsis MAX2, rice D3and petunia RMS4genes which are involved in the signaltransduction of the novel hormone strigolactones, a suppressor of shoot branching.Thefull-length cDNA is2,463bp in length, including a CDS region of2109bp, a5’ UTR of56bp and a3’UTR of298bp. The genomic DNA of the putative GhMAX2gene does notcontain an intron and encodes702amino acids. Furthermore, two highly similar sequencesof the putative GhMAX2gene were obtained, showing only31bp difference in the CDSregion and15amino acids difference at the protein level. We respectively name them asGhMAX2a and GhMAX2b. By alignment of the deduced amino acid sequence of theGhMAX2a/b with other functionally characterized homologous proteins such as theArabidopsis MAX2, pea RMS4and rice D3, two functional domains are identified in theGhMAX2a/b protein: an F-box motif at the N-terminus and a LRR domain containing18imperfect leucine rich repeats at the C-terminal part. In order to study the evolutionaryrelationships among the predicted MAX2proteins, a phylogenetic tree was constructedusing MAX2proteins from a taxonomically diverse set of species. These proteins weregrouped into3clades: the lower plant, monocotyledon, and dicotyledon. Within thedicotyledon clade, GhMAX2a/b is most close to the castor bean couterpart. Sequencealignment and phylogenetic tree analysis indicate that we have cloned the MAX2homologfrom upland cotton. Two constructs consisting of the GhMAX2full-length cDNA driven bythe CaMV35S promoter is introduced into the Arabidopsis thaliana max2mutant. Ectopicexpression of both GhMAX2a and GhMAX2b in the dwarfed and highly-branched max2-1Arabidopsis mutant resulted in recovery of normal growth indicating that GhMAX2s are functional orthologs of AtMAX2. One construct consisting of the GhMAX2full-lengthcDNA is introuced into pGADT7. Unequal expression was detected between thisduplicated gene pair where the expression level of GhMAX2b is about three times than thatof GhMAX2a. In order to know whether their cotton homolog GhMAX2is responsive toGR24as the MAX2/RMS4/D3or not, we treated the cotton seedlings with differentconcentration of GR24for different time period. Transcript level of GhMAX2is examined by RT-PCR analysis. The result showes that no matter low or highconcentration, short-or long-term treatment, the GhMAX2transcript level does not varyremarkably. This result indicates that transcription of GhMAX2is not responsive tostrigolactone. Seven construsts consisting of the GhMAX2full-length, the F-box, the LRRs,the ASK1, OSK15are respectly used for yeast two-hybrid assays and Co-IP. These datashow that GhMAX2can interact with ASK1and participate in an SCF complex. Theseresults suggest that the cotton GhMAX2genes encode functional MAX2isoforms that caninhibit the shoot lateral branching. Further analyses of the function of GhMAX2genes andtheir possible roles in determining cotton plant architecture and yield are underway. |
PDF Full Text Request