Gibberellin biosynthesis and signal transduction is essential for internode elongation in deepwater rice

Abstract

Under flooded conditions, the leaves and internodes of deepwater rice can elongate above the water surface to capture oxygen and prevent drowning. Our previous studies showed that three major quantitative trait loci (QTL) regulate deepwater-dependent internode elongation in deepwater rice. In this study, we investigated the age-dependent internode elongation in deepwater rice. We also investigated the relationship between deepwater-dependent internode elongation and the phytohormone gibberellin (GA) by physiological and genetic approach using a QTL pyramiding line (NIL-1 + 3 + 12). Deepwater rice did not show internode elongation before the sixth leaf stage under deepwater condition. Additionally, deepwater-dependent internode elongation occurred on the sixth and seventh internodes during the sixth leaf stage. These results indicate that deepwater rice could not start internode elongation until the sixth leaf stage. Ultra-performance liquid chromatography tandem mass-spectrometry (UPLC-MS/MS) method for the phytohormone contents showed a deepwater-dependent GA1 and GA4 accumulation in deepwater rice. Additionally, a GA inhibitor abolished deepwater-dependent internode elongation in deepwater rice. On the contrary, GA feeding mimicked internode elongation under ordinary growth conditions. However, mutations in GA biosynthesis and signal transduction genes blocked deepwater-dependent internode elongation. These data suggested that GA biosynthesis and signal transduction are essential for deepwater-dependent internode elongation in deepwater rice.Deepwater rice obtained the ability for rapid internode elongation to avoid drowning and adapt to flooded condition. How does it regulate internode elongation? Using both physiological and genetic approach, this paper shows that the plant hormone, gibberellin (GA) regulates internode elongation.

Group VII Ethylene Response Factors Coordinate Oxygen and Nitric Oxide Signal Transduction and Stress Responses in Plants

“…Furthermore, there is a strong up-regulation of GA-deactivating GA 2-oxidase in SUB1A-containing lines, which would reduce the levels of active GA and enhance SLR1 stability (Jung et al, 2010). In contrast, during flooding in deep-water rice varieties, the induction of SNORKEL1 and SNORKEL2 by ethylene triggers internode elongation by up-regulating GA 20-oxidase, which increases the accumulation of active GA (Raskin and Kende, 1984;Hattori et al, 2009;Ayano et al, 2014). Similar quiescent and escape-like flooding responses have also recently been identified in two related Rumex spp.…”

Ethylene-Mediated Acclimations to Flooding Stress

“…How signaling from the SKs leads to downstream events culminating in shoot elongation is unclear. Quantitative trait loci analyses on GA-controlled responses of deep-water rice internodes indicate that signaling downstream of the SKs and the other uncharacterized quantitative trait loci regions coordinately affects GA biosynthesis (Ayano et al, 2014;Nagai et al, 2014).…”

MOLECULAR BASIS OF THE DWARFISM CHARACTER IN CULTIVATED PLANTS. I. GROWTH DISTORTIONS DUE TO MUTATIONS OF GIBBERELLIN METABOLISM AND SIGNALING (review)

“…GA-insensitive, dwarf [20,24,25] Rice d1 G (-subunit of heterotrimeric G-Enzyme, GTPase, EC 3.6.5.1)…”

“…In plants of the second group the growth changes may be associated with disorders in gibberellic signal perception and transduction to GA-inducible genes. This group, unlike the first one, is characterized by a reduced response or insensitivity to GA. [28] (as amended): GGDP -geranylgeraniol diphosphate, GA 1-110 -gibberellins; CPS -ent-copalyl diphosphate synthase, KS -entkaurene synthase, KO -ent-kaurene oxidase, KAO -ent-kaurenoic acid oxidase; 13ox -monooxygenase hydroxylating gibberellic GA 12 aldehyde at C13 position; GA20ox, GA3ox and GA2ox -three groups of 2-oxoglutarate-dependent dioxygenases (GA 20 (Fig. 1), which is also the precursor for carotenoids and unsaturated phytol, a diterpene alcohol forming part of chlorophyll.…”

“…One group of these enzymes is GA 20 -oxidases (GA20ox), and the other group is the C3,β-oxidases (GA3ox, or C3,β-hydroxylases), of which the former oxidize C 20 -gibberellins to C 19 -gibberellins, and the latter catalyze hydroxylation of GA molecules at C3,β position at the final stage of the biosynthetic pathway. Rice mutants with deactivated GA3ox and GA20 genes were stunted [13,34].…”