Given the important roles of miRNAs in post-transcriptional gene regulation, identification of differentially expressed miRNAs will facilitate the elucidation of molecular mechanisms underlying kernel development. In this study, we constructed a small RNA library to comprehensively represent the full complement of individual small RNAs and to characterize miRNA expression profiles in pooled ears of maize(Zea mays L.) at 10, 15,20, 22, 25 and 30 days after pollination(DAP). At least 21 miRNAs were differentially expressed. The differential expression of three of these miRNAs, i.e., miR528a, miR167a and miR160b, at each stage was verified by qRT-PCR. The results indicated that these miRNAs might be involved in kernel development. In addition, the predicted functions of target genes indicated that most of the target genes are involved in signal transduction and cell communication pathways, particularly the auxin signaling pathway. The expression of candidate germination-associated miRNAs was analyzed by hybridization to a maize genome microarray, and revealed differential expression of genes involved in plant hormone signaling pathways. This finding suggests that phytohormones play a critical role in the development of maize kernels. We found that in combination with other miRNAs, miR528a regulated a putative laccase, a Ring-H2 zinc finger protein and a MADS box-like protein, whereas miR167a and miR160b regulated multiple target genes,including ARF(auxin response factor), a member of the B3 transcription factor family. All three miRNAs are important for ear germination, development and physiology. The small RNA transcriptomes and mRNA obtained in this study will help us gain a betterunderstanding of the expression and function of small RNAs in the development of maize kernel.
The authors cloned and identified a new maize serine carboxypeptidase gene named ZmSCP from R15 inbred lines seedlings which were induced by Rhizoctonia solani AGI-IA. ZmSCP encodes a 332 amino acid protein with a predicted molecular mass of 36.5 kDa and pI of 4.75. Phylogenetic analysis revealed that ZmSCP showed closer kinship with Oryza sativa and sorghum, which belong to the same evolutionary branch. Amino acid sequence analysis revealed that there are four types of amino acids in ZmSCP, the percentages of them are 43.1%, 26.9%, 13.9% and 13.1%. The authors subsequently purified the recombinant protein which expressed in Escherichia coli BL21 and analyzed its antimicrobial activities in vitro. Results showed that the recombinant protein inhibited hyphal growth of Rhizoctonia solani. The study suggests that the expression of ZmSCP is closely related to maize sheath blight resistance caused by Rhizoctonia solani. Further, the antifungal activity showed that ZmSCP may play at role in the disease resistance response.
Li LiuXiujing HeZhiming ZhangMaojun ZhaoJing WangHaijian LinYa'ou ShenlGuangtang Pan
