Abstract
BackgroundThe inferior spikelets are defined to be those at portions where the grains receive less photosynthetic products during the seed development. The typical inferior spikelets are physically located on the proximal secondary branches in a rice panicle and traditionally characterized by a later flowering time and a slower grain-filling rate, compared to those so-called superior spikelets. Grains produced on the inferior spikelets are consequently under-developed and lighter in weight than those formed on the superior spikelets. MicroRNAs (miRNAs) are recognized as key players in regulating plant development through post-transcriptional gene regulations. We previously presented the evidence that miRNAs may influence grain-filling rate and played a role in determining the grain weight and yield in rice.ResultsIn this study, further analyses of the expressed small RNAs in superior and inferior spikelets were conducted at five distinct developmental stages of grain development. Totally, 457 known miRNAs and 13 novel miRNAs were analyzed, showing a differential expression of 141 known miRNAs between superior and inferior spikelets with higher expression levels of most miRNAs associated with the superior than the inferior spikelets during the early stage of grain filling. Genes targeted by those differentially expressed miRNAs (i.e. miR156, miR164, miR167, miR397, miR1861, and miR1867) were recognized to play roles in multiple developmental and signaling pathways related to plant hormone homeostasis and starch accumulation.ConclusionsOur data established a complicated link between miRNA dynamics and the traditional role of hormones in grain filling and development, providing new insights into the widely accepted concepts of the so-called superior and inferior spikelets in rice production.
Highlights
The inferior spikelets are defined to be those at portions where the grains receive less photosynthetic products during the seed development
Physiological and phenotypic differences between superior and inferior spikelets In general, the rice grain filling processes were dynamic in spikelets according to their locations on the rachis/ panicle branches
Superior spikelets are on the top of the panicle, always flower earlier, have grains filling faster, and the higher final grain weight and plumpness than the inferior spikelets which are located on the base of the panicle [3,6,7]
Summary
The inferior spikelets are defined to be those at portions where the grains receive less photosynthetic products during the seed development. The yield of rice is determined primarily by two vital factors, the grain filling rate and subsequently the grain weight [2]. It has been demonstrated by many researches that are located on the proximal secondary branches, resulting in low-quality seeds [3,6,7]. The expressions of most known miRNAs increased gradually as rice grain filling went on [16] These observations were in contrast to another study showing that about half of the known miRNAs were up-regulated, while the remaining miRNAs were down-regulated during indica rice grain development [18]
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