Developmental Course of Inflorescence and Spikelet in Rice

Abstract

Seed production in rice (Oryza sativa L.) largely depends on the number of flowers, which is in turn regulated by the inflorescence architecture. The developmental process of inflorescence and spikelet in grasses including rice differs considerably from that in other monocotyledonous and dicotyledonous species, and rice, an important crop plant, is often used as a model monocot plant. Nevertheless, the developmental course of wild-type rice has not yet been well characterized. Thus, detailed description of rice inflorescence and spikelet development would be valuable for characterizing mutant phenotypes and also for comparing rice with other grass species. In this study, we showed a number of landmark events in the developmental courses of inflorescence and spikelet, and divided their development into nine and eight stages, respectively. This staging system would be useful as a reference for developmental description.

The AGL6-like gene OsMADS6 regulates floral organ and meristem identities in rice

“…To be in line with previous observations, we used the developmental stages defined by Ikeda et al [33]. Till stage Sp4, the primordia of the lemma/palea and empty glumes looked the same in wild type and osmads6-1 floral primordia (Figure 2A and 2E).…”

“…Each rice spikelet consists of a flower with one pistil, six stamens and two lodicules subtended by an inner bract or prophyll, called as the palea, and an outer bract called the lemma. In addition, each spikelet contains two highly reduced leaf-like rudimentary glumes at the base in a distichous pattern, and two depressed empty glumes at a position opposite to each other above the rudimentary glumes [33]. Here, we show that OsMADS6 is a key regulator that controls the development of rice flower organs, but does not affect the development of the lemma, empty glumes and rudimentary glumes.…”

Rice DENSE AND ERECT PANICLE 2 is essential for determining panicle outgrowth and elongation

“…The third step is the differentiation of floral organs such as glume, lodicules, stamen, and carpel. After all floral organs are differentiated, rachis and branches begin to elongate exponentially till heading, reaching the full length [17]. To date, most of the identified genes affecting panicle architecture are involved in the establishment of inflorescence meristems, while little is known about the molecular basis of the outgrowth and elongation of branches.…”

“…Development of rice inflorescence is categorized into nine stages. Proximal primary branch primordia, in spite of earlier formation, seem not to elongate until the last primordium is formed, and all the primordia almost simultaneously start to elongate at In 8, when the length of inflorescences reaches 40 mm and differentiation of all floral organs is finished [17]. On the basis of these categories, we may conclude that the erect panicle in dep2 was caused during the late stage of panicle development, while the formation of primordia and differentiation of spikelets were not affected in young panicle development.…”

“…Interestingly, rapid elongation of the panicle does not start until stage In 8 [17], when inflorescence meristems abort and all floral organs, like primary branches, secondary branches, and spikelets, are differentiated. Currently, several genes involved in the formation or initiation of floral meristems have been isolated [18][19][20][21][22][23][24].…”