Stomatal Development and Gene Expression in Rice Florets

Abstract

Stomata play a fundamental role modulating the exchange of gases between plants and the atmosphere. These microscopic structures form in high numbers on the leaf epidermis and are also present on flowers. Although leaf stomata are well-studied, little attention has been paid to the development or function of floral stomata. Here, we characterise in detail the spatial distribution and development of the floral stomata of the indica rice variety IR64. We show that stomatal complexes are present at low density on specific areas of the lemma, palea and anthers, and are morphologically different compared to stomata found on leaves. We reveal that in the bract-like organs, stomatal development follows the same cell lineage transitions as in rice leaves, and demonstrate that the overexpression of the stomatal development regulators OsEPFL9-1 and OsEPF1 leads to dramatic changes in stomatal density in rice floral organs, producing lemma with approximately twice as many stomata (OsEPFL9-1_oe), or lemma where stomata are practically absent (OsEPF1_oe). Transcriptomic analysis of developing florets also indicates that the cellular transitions during the development of floral stomata are regulated by the same genetic network used in rice leaves. Finally, although we were unable to detect an impact on plant reproduction linked to changes in the density of floral stomata, we report alterations in global gene expression in lines overexpressing OsEPF1 and discuss how our results reflect on the possible role(s) of floral stomata.

Stomatal density affects rice mesophyll cell size and shape and modulates a conserved pattern of cells through the leaf

“…To see if leaves with increased stomatal conductance also displayed a mesophyll phenotype, two transgenic rice lines overexpressing EPFL9 were used: OsEPFL9OE-2 and OsEPFL9OE-3 (Bertolino et al ., 2022). Compared to IR64, these lines had a significantly higher stomatal conductance ( Fig.…”

Photosynthesis – beyond the leaf

“…Therefore, manipulating SD (e.g. Bertolino et al, 2022) or function (Lawson & Matthews, 2020) in wheat ears alone could improve heat tolerance and support greater photosynthesis through increased evaporative cooling, influence translocation of photoassimilates and nutrients to the grains and provide a route to improve nonfoliar water-use efficiency. New Phytologist (2023) www.newphytologist.com…”

“…3; Hu et al, 2019;Henry et al, 2020;Simkin et al, 2020), and certain fruits (Brazel & Ó'Maoiléidigh, 2019); however, their functionality, including their contribution to carbon acquisition, has not been fully evaluated (Simkin et al, 2020). Recent work by Bertolino et al (2022) has reported considerable spatial variation in stomata in rice floral organs and suggested that they are morphologically distinct from leaf stomata, although their function is still unknown.…”

“…However, to date, the majority of these studies have focused on leaves, and few have considered the contribution from other tissues (Simkin et al ., 2020 ). Green tissues other than leaves, including stems (Simkin et al ., 2020 ), ears/panicles (Maydup et al ., 2014 ; Rivera‐Amado et al ., 2020 ; Zhang et al ., 2022 ), green floral organs (Bertolino et al ., 2022 ), pods (Wang et al ., 2016 ) and fruit (Simkin et al ., 2020 ), have been reported to photosynthesize and contribute to varying degrees and to overall plant carbon gain. Wheat and rice panicles, which a large proportion of studies have focused on, have been reported to have high photosynthetic capacities (Brazel & Ó'Maoiléidigh, 2019 ; Chang et al ., 2020 ; Sanchez‐Bragado et al ., 2020 ), with panicle and ear photosynthesis reported to contribute between 10% and 60% to yield (Hu et al ., 2019 ) and spike photosynthesis positively correlated with yield (Molero & Reynolds, 2020 ).…”

Rice mutants, selected under severe drought stress, show reduced stomatal density and improved water use efficiency under restricted water conditions

“…Transpiration is controlled by several thousand microscopic porous organs called stomata, which are found in all plant leaves and floral parts. These organs are distributed throughout the phyllosphere, including leaf surfaces, leaf sheaths (stems), floral parts and even tiny anthers ( Bertolino et al., 2022 ). Stomatal traits vary between eudicots and monocots.…”