Abstract
Floral transition and petal onset, as two main aspects of flower development, are crucial to rapeseed evolutionary success and yield formation. Currently, very little is known regarding the genetic architecture that regulates flowering time and petal morphogenesis in Brassica napus. In the present study, a genome-wide transcriptomic analysis was performed with an absolutely apetalous and early flowering line, APL01, and a normally petalled line, PL01, using high-throughput RNA sequencing. In total, 13,205 differential expressed genes were detected, of which 6111 genes were significantly down-regulated, while 7094 genes were significantly up-regulated in the young inflorescences of APL01 compared with PL01. The expression levels of a vast number of genes involved in protein biosynthesis were altered in response to the early flowering and apetalous character. Based on the putative rapeseed flowering genes, an early flowering network, mainly comprised of vernalization and photoperiod pathways, was built. Additionally, 36 putative upstream genes possibly governing the apetalous character of line APL01 were identified, and six genes potentially regulating petal origination were obtained by combining with three petal-related quantitative trait loci. These findings will facilitate understanding of the molecular mechanisms underlying floral transition and petal initiation in B. napus.
Highlights
Genes underwent two vital duplication and divergence events that orderly generated the PI, paleoAP3, euAP3 and TM6 lineages, and the appearance of euAP3 lineage was closely related to petal origin in higher eudicots[15,16]
Unlike line PL01, the petal primordial of line APL01 do not appear in the second whorl (Fig. 1C), suggesting that the apetalous character of line APL01 is formed at the initial petal primordia stage
The remaining floral organs of line APL01 are fully developed, which distinguishes the line from apetalous mutants of Arabidopsis and Antirrhinum with variant sepals or stamens[7,8], leading to the speculation that the regulation of genes that downstream ABC class genes in petal development pathways might have been changed[12]
Summary
Genes underwent two vital duplication and divergence events that orderly generated the PI, paleoAP3, euAP3 and TM6 lineages, and the appearance of euAP3 lineage was closely related to petal origin in higher eudicots[15,16]. Unlike all of the apetalous mutants in Arabidopsis and Antirrhinum, the number and morphology of sepals, stamens and carpels of many apetalous rapeseeds detected in earlier studies are similar to those of the natural variety[33,34], seemingly indicating that the genetic mechanism governing petal development of rapeseed is not completely consistent with the model plants at some level. The rapeseed lines APL01 and PL01, two lines with distinguishable flowering time and petal morphologies, were used for Illumina RNA-seq to study the differential expressed genes (DEGs) in the young inflorescences. In combination with gene ontology (GO)-enrichment analysis and homologous alignments, the discovery of the molecular basis underlying early flowering and apetalous characteristic in line APL01 is expected. The detection of potential candidate genes regulating the petalous degree (PDgr) of rapeseed is expected to be assisted by coupling RNA-seq with QTL mapping
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