Linking Auxin with Photosynthetic Rate via Leaf Venation

International audienceLand plants lose vast quantities of water to the atmosphere during photosynthetic gas exchange. In angiosperms, a complex network of veins irrigates the leaf, and it is widely held that the density and placement of these veins determines maximum leaf hydraulic capacity and thus maximum photosynthetic rate. This theory is largely based on interspecific comparisons and has never been tested using vein mutants to examine the specific impact of leaf vein morphology on plant water relations. Here we characterize mutants at the Crispoid (Crd) locus in pea (Pisum sativum), which have altered auxin homeostasis and activity in developing leaves, as well as reduced leaf vein density and aberrant placement of free-ending veinlets. This altered vein phenotype in crd mutant plants results in a significant reduction in leaf hydraulic conductance and leaf gas exchange. We find Crispoid to be a member of the YUCCA family of auxin biosynthetic genes. Our results link auxin biosynthesis with maximum photosynthetic rate through leaf venation and substantiate the theory that an increase in the density of leaf veins coupled with their efficient placement can drive increases in leaf photosynthetic capacity

Surviving a Dry Future: Abscisic Acid (ABA)-Mediated Plant Mechanisms for Conserving Water under Low Humidity

Angiosperms are able to respond rapidly to the first sign of dry conditions, a decrease in air humidity, more accurately described as an increase in the vapor pressure deficit between the leaf and the atmosphere (VPD), by abscisic acid (ABA)-mediated stomatal closure. The genes underlying this response offer valuable candidates for targeted selection of crop varieties with improved drought tolerance, a critical goal for current plant breeding programs, to maximize crop production in drier and increasingly marginalized environments, and meet the demands of a growing population in the face of a changing climate. Here, we review current understanding of the genetic mechanisms underpinning ABA-mediated stomatal closure, a key means for conserving water under dry conditions, examine how these mechanisms evolved, and discuss what remains to be investigated

Update on the genetic control of flowering in garden pea.

International audienceThe garden pea has been a model for the genetics of flowering for several decades and numerous flowering loci have been identified, but until recently little was known about the molecular nature of these loci. This paper presents an update on recent work on the molecular genetics of flowering in pea, outlining progress in gene and mutant isolation, expression analyses, grafting and other physiological studies, and candidate gene assessment. Work so far has led to the identification of the LATE1 and DNE loci as orthologues of Arabidopsis GIGANTEA and ELF4, respectively, and candidate genes for several other loci are being evaluated. Expression analysis of an expanded FT-like gene family suggests a more complex role for this group of genes. These results provide the first insight into the circadian clock, photoperiod response mechanism, and mobile signals in pea, and identify both conserved and divergent features in comparison with Arabidopsis

Identification of LATE BLOOMER2 as a CYCLING DOF FACTOR Homolog Reveals Conserved and Divergent Features of the Flowering Response to Photoperiod in Pea

BAPGEAPSISUPDATThe molecular pathways responsible for the flowering response to photoperiod have been extensively studied in Arabidopsis thaliana and cereals but remain poorly understood in other major plant groups. Here, we describe a dominant mutant at the LATE BLOOMER2 (LATE2) locus in pea (Pisum sativum) that is late-flowering with a reduced response to photoperiod. LATE2 acts downstream of light signaling and the circadian clock to control expression of the main photoperiod-regulated FT gene, FTb2, implying that it plays a primary role in photoperiod measurement. Mapping identified the CYCLING DOF FACTOR gene CDFc1 as a strong candidate for LATE2, and the late2-1D mutant was found to carry a missense mutation in CDFc1 that impairs its capacity to bind to the blue-light photoreceptor FKF1 in yeast two-hybrid assays and delays flowering in Arabidopsis when overexpressed. Arabidopsis CDF genes are important negative regulators of CONSTANS (CO) transcription, but we found no effect of LATE2 on the transcription of pea CO-LIKE genes, nor on genes in any other families previously implicated in the activation of FT in Arabidopsis. Our results reveal an important component of the pea photoperiod response pathway and support the view that regulation of FTb2 expression by photoperiod occurs via a CO-independent mechanism

The Pea GIGAS Gene Is a FLOWERING LOCUS T Homolog Necessary for Graft-Transmissible Specification of Flowering but Not for Responsiveness to Photoperiod[C][W]

The pea flowering gene GIGAS regulates a mobile flowering signal and is essential for flowering under long days but not for the ability to respond to photoperiod. This study characterizes the FLOWERING LOCUS T (FT) gene family in pea, identifies one gene (FTa1) as GIGAS, and associates another gene (FTb2) with a second mobile signal and a broader role in photoperiod responsiveness

VEGETATIVE1 is essential for development of the compound inflorescence in pea

[EN] Unravelling the basis of variation in inflorescence architecture is important to understanding how the huge diversity in plant form has been generated. Inflorescences are divided between simple, as in Arabidopsis, with flowers directly formed at the main primary inflorescence axis, and compound, as in legumes, where they are formed at secondary or even higher order axes. The formation of secondary inflorescences predicts a novel genetic function in the development of the compound inflorescences. Here we show that in pea this function is controlled by VEGETATIVE1 (VEG1), whose mutation replaces secondary inflorescences by vegetative branches. We identify VEG1 as an AGL79-like MADS-box gene that specifies secondary inflorescence meristem identity. VEG1 misexpression in meristem identity mutants causes ectopic secondary inflorescence formation, suggesting a model for compound inflorescence development based on antagonistic interactions between VEG1 and genes conferring primary inflorescence and floral identity. Our study defines a novel mechanism to generate inflorescence complexity.We thank Christine Le Signor for sending the seed from the pea TILLING lines, and to Miguel Blazquez for critical reading of the manuscript. This work was supported by grants from Spanish Ministerio de Ciencia e Innovacion (BIO2009-10876 to F. M. and BIO2009-09920 to C. F.), the Conselleria d'Empresa Universitat i Ciencia from the Generalitat Valenciana (GV03-066 to F. M., C. F. and J.P.B.), the EU-FP6 (GL-IP, FP6-2002-FOOD-1-506223, to F. M., C. F., J.P.B., T.H.N.E and A. Bendahmane), the EU-FP4 (EUdicotMap, BIOCT972170, to T.H.N.E. and S. A. T.), the Australian Research Council (Discovery Project DP6556508 to J.L.W., V. H. and F. C. 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